The only time when matza must be eaten to fulfill the commandment of eating matza is on seder night(s). There may be a mitzva to also eat matza on the other days of Passover (but there are conflicting opinions about that).
However, men must eat matza in order to fulfill the commandment of eating two meals a day on each of the festival days.
 

The minimum amount of water to remove tum'a (ritual impurity) is 3.3 fl. oz. (99 ml, or 1 revi'it) total, for both hands.

Tachanun is related to judgment. Tachanun is NOT said at times of din/judgment:

• At night,
• On Tish'a B'Av,
• In a house of mourning, and
• Yom Kippur.

Tachanun is also NOT said at times of simcha/happiness:

• Shabbat,
• Jewish festivals,
• Rosh Hashana, and
• Rosh Chodesh.

• Isru chag (the day after each of the Jewish festivals),
• Entire month of Nisan.

• All of Chanuka, Purim, Shushan Purim, Tu B'Shvat, Rosh Chodesh, and from Rosh Chodesh Sivan until the day after Shavuot.
• Tishrei from shacharit before Yom Kippur until after Simchat Torah (Shmini Atzeret in Eretz Yisrael). Resume saying tachanun:
  • Second day of Cheshvan, or
  • Day after isru chag of Simchat Torah (this is the more prevalent custom among Ashkenazim). Each person should follow his or her family or community custom.

• Mohel,
• Sandak, or
• Father of a boy having his circumcision.

Bal Tashchit May Override Custom
You may not destroy things in the world for no purpose. You may not waste anything (bal tashchit) that has a use, but you may use it for a purpose. Bal tashchit overrides customs and suggestions of what are good behaviors or actions.
Killing Creatures that Harm
You may kill any animal, bird, or other living creature that bothers, injures, or endangers people or destroys property (as long as it is legal by the laws of the local country or area). This includes animals that eat your food or produce.

Shavuot (Yom HaBikurim in the Torah) celebrates and commemorates the giving of the Ten Commandments to the Israelites at Mt. Sinai.
Beginning with the second night of Passover, the Israelites who left Egypt underwent 49 days of spiritual improvement and purification until they were ready to receive the Torah from God (Shavuot ends this 49-day “omer” period).  We can undergo a similar process of spiritual development each year during these 49 days (how to do that is beyond the scope of this website). According to our tradition, the Israelites in Egypt had sunk to the 49^th level of spiritual impurity (tum'a). The Israelites had to raise themselves in 49 daily stages to be worthy of receiving the Torah.  Several books and siddurs portray the 49 days of the omer as corresponding to the Seven Sefirot embedded in the seven weeks.  This awareness can help us work on and maximize the power inherent in each day of the omer to fix that particular sefira in ourselves. We thus relive this transition from slavery to freedom and the service of God each year as we try to perfect our midot (personal characteristics) to again be worthy of receiving the Torah on Shavuot.

 
Symbolism of the Shavuot Offering
In the Temple in Jerusalem, the only communal sacrifice of leavened bread was on Shavuot. Leavening in dough is compared to arrogance in humans (people puff themselves up to look more important than they actually are). During Passover we destroy, and refrain from eating, leaven--just as we try to destroy/remove arrogance from our personalities. After Passover, we continue to work on our personal traits (midot) until we reach Shavuot, when we celebrate receiving the Torah.  At Shavuot, we Jews have a right to feel important, since we are spiritually elevated by virtue of having been given the Torah.
 
Shavuot: Universal Customs
The universal custom is to eat at least one dairy food during Shavuot.
Possible reason  At the time the Israelites received the Torah, they did not have any kosher meat (they had not been required to eat kosher until then) and so the only food they were permitted to eat was dairy food.
Another universal custom is to stay awake all night (if possible) studying Torah.
 
Shavuot: Symbols
Unlike other Jewish festivals, Shavuot has no concrete symbols and no specific unique commandments/mitzvot, other than sacrifices that were brought in the Temple in Jerusalem.

The minimum size for the garment of a talit katan is large enough to wrap your torso in, in front and in back: 17 inches (43 cm) wide and 17 inches (43 cm) long, from the top edge to bottom edge and so the total minimum dimensions will be 17 inches wide by 34 inches long. The optimal size is 24 inches wide and 24 inches long on each side (resulting in dimensions of 24 inches by 48 inches. 

The seder is the only time in the year that you must drink most of your cup (rov kos) of kiddush wine. (For kiddush on Shabbat and Jewish festivals, you need drink only 2 fl. oz., or 59 ml).  So if you have a cup larger than 4 fl. oz. (119 ml), you may have to drink a lot of wine--more than half of each cup for four cups! 

Choose the correct smell blessing (Note that these blessings are not said on synthetic scents!): 

• Borei minei vesamim Generic; this is the default blessing if you are not certain which category applies; also say this when smelling a mixture of scents;
• Borei isvei vesamim  Plants which do not have stiff stems;
• Borei atzei vesamim  Trees and stiff-stemmed plants (such as roses); and
• Ha'notein rei'ach tov ba'peirot  Fragrant fruits, such as lemons and some etrogs.

1 Revi'it = Usually 3.3 fl. oz. (99 ml); but 4 fl. oz. (119 ml) for:

• Any food requiring bracha achrona.
• The four cups of wine at the seder.
• Kiddush for Shabbat and Jewish festival nights.

 
1 Log = Volume of 6 eggs = 4 Revi'ot (a revi'it is 1/4 of a log)  
1 Kab = 4 Login  
1 Se'ah = 6 Kabin
 
40 Se'ah = Volume equivalent to 3 cubes, 24 ½” (61 cm) on each side; minimum requirement for mikva = about 192 gallons/750 liters  

1 fl. oz. = 1.77 cu. inch (about the size of a golf ball)

Rosh Chodesh, the beginning of the Jewish (lunar) month, is a minor holiday of one or two days, depending on whether the previous month was 29 or 30 days.  When the preceding month is 30 days long, the 30th day becomes the first day of Rosh Chodesh and the second day of Rosh Chodesh is the first day of the succeeding month.
Rosh Chodesh used to be officially declared in Jerusalem each month by the Sanhedrin, based on evidence from at least two witnesses who had seen the new moon in the western sky.  For the past 1700 years or so, the new moon (and the dates for the entire Jewish calendar) have been determined by a formula prescribed by Hillel HaNasi (then head of the Jewish community in Eretz Yisrael). 

If you take off your tefilin because you have to, such as to go to the bathroom, or if one or both of the tefilin fall or slide off your arm or head, say: 

• Both blessings again when you replace the head tefila (tefila shel rosh) on your head.
• Only the first blessing when replacing the arm tefila (tefila shel yad) on your arm.
• Each blessing in its correct place if you took off both.

You may use any nice-smelling substance for havdala “besamim,” not just spices; but the source of the scent must be natural. There is no priority for using cinnamon.

Note For besamim, you may scratch a lemon or orange or other aromatic fruit and sniff the fruit itself (but not your hand). However, say the normal havdala blessing, borei minei v'samim, instead of the normal blessing for smelling fruits (ha'notein rei'ach tov ba'peirot).
 

Three Shabbat Meals
We are required to eat three Shabbat meals, as a rabbinic (d'rabanan) enactment to enjoy Shabbat (oneg Shabbat). The first Shabbat meal must be at night and the remaining two must be during the day (the third meal must be eaten after halachic midday). Friday night dinner and the first meal on Saturday are preceded by kiddush. For the first two Shabbat meals, say ha'motzi over two complete loaves of bread, each of which is at least 1.3 fl. oz. in volume. For the third meal, the ideal is to use two complete loaves of bread, but the requirement of eating the third meal can also be fulfilled by eating any food other than salt or water.

Source of Saying Shabbat Kiddush

• Saying kiddush on Shabbat night is a commandment from the Torah (d'oraita).
• Saying kiddush on Saturday morning is a rabbinical (d'rabanan) enactment.

Note If you did not say Friday night kiddush, you must say that version of kiddush on Shabbat morning and it is then a requirement from the Torah (d'oraita). Do not begin with va'yechulu; instead, begin with borei pri ha'gafen and say the second blessing of kiddush.

Source of Kiddush Location
Saying kiddush at the place where you will eat your meal is a rabbinical (d'rabanan) enactment.

Shabbat Kiddush-Meal Quantities: Evening

• For evening kiddush, a minimum of 4 fl. oz. (119 ml) of wine must be blessed on and at least half must be drunk.
• For the evening meal, as on Shabbat lunch and all required Jewish festival meals, a minimum of 1.9 fl. oz. of bread must be eaten within four minutes.

Shabbat Kiddush-Meal Quantities: First Meal on Saturday
Shabbat day first meal has two separate eating requirements.  They may be combined (say/hear kiddush and start the main meal right away) but are often done separately (say/hear kiddush and then eat some mezonot; the main meal is eaten later in the day).
Note Since eating and drinking requirements on all morning kiddushes (both Shabbat and Jewish festivals) are d'rabanan, the required beverage amount for morning kiddush is only 3.3 fl. oz. (99 ml) instead of the d'oraita 4 fl. oz. (119 ml), which is required for kiddushes for Shabbat evening.
1) Morning kiddush requires a halachically legal “meal” with these elements:
      a) Blessing on a minimum of 3.3 fl. oz. (99 ml) of wine (or other beverage),
      b) Someone's drinking at least 2 fl. oz. of the beverage, followed by
      c) Eating at least 1.3 fl. oz. (39 ml, or 1/6 cup) of some type of mezonot (or bread) within four minutes.
Note If you drink at least 3.3 fl. oz. (99 ml) of wine within 30 seconds, you do not need to eat mezonot.
Note You do not need to drink the wine or other kiddush beverage to fulfill “establishing a meal.” You may hear kiddush and then simply eat the required amount of bread or mezonot. This applies to Shabbat or Jewish festivals, evening or morning.
The kiddush “meal” does not have to satiate.
Note If you have not fulfilled the requirements for kiddush, you may not eat other foods, such as fruit or fish at a kiddush.

2) The real meal (kovei'a se'uda) of Shabbat lunch requires eating at least 1.9 fl. oz. (56 ml) of bread (or matza during Passover!) within four minutes. It should include enough food to satiate.
Note You can simultaneously fulfill the requirement to “establish a meal” and to “eat a meal” by eating one (the same) piece of bread.
For details on fulfilling the first two meals' requirements, see Shabbat: Kiddush.

Shabbat: Eating a Meal Requirement: Third Meal
For details on fulfilling the third meal's requirements, see Shabbat: Third Meal (Se'uda Shlishit).

WERE BOTH FOODS LESS THAN 120° F?
YES

ARE BOTH FOODS SOLID?
YES
Status If you can separate them (there are no cracks in the meat), both foods are kosher.  Consult a rabbi.
What to Do

• If one or both of the foods were already cooked, separate them and wash with soap and water (if possible).
• If it is not possible to separate them, just cut off the thinnest slice possible from each surface of each food which had been in contact with the opposite gender food and you may use the food.

NO
SOLID FOOD FALLS INTO LIQUID FOOD OR LIQUID FOOD FALLS ONTO SOLID FOOD
Status If both foods are cold and you can separate them (there are no cracks in the meat), they MAY be kosher.  Consult a rabbi.
 

• Both foods are non-kosher if they cannot be separated.
• If you can separate them enough that one becomes less than 1/60th the volume of the other:
  • The larger food is kosher.
  • The lesser one is non-kosher. 

What To Do

• Once the two foods are separated, wash or otherwise remove the smaller food from the larger one.
• If not possible, cut off the thinnest slice possible and you may eat the remaining food.

Note If there are cracks in raw or cooked meat, and if you can clean off enough of the dairy spill so that the remainder is less than 1/60th, it may be kosher--ask a rabbi.
 
LIQUID FOOD FALLS INTO LIQUID FOOD
Status Both liquid foods are non-kosher.
Exception If one liquid food is less than 1/60th the volume of the other one, the mixture is kosher.
Note If non-kosher wine is involved, see below.
 
SOLID FOODS, ONE OR BOTH ARE HOT
Status If one (or both) of the foods is hotter than 120° F, both foods are non-kosher.
Exception If one food is less than 1/60th of the volume of the other:

• The larger-volume food may be kosher (consult a rabbi).
• The smaller-volume food remains not kosher.

Possible Exception  If the food on the bottom is cold and thick, consult a rabbi.

If either food is spicy, see above.
If any combination (solid and liquid; solid and solid which are in any liquid; or liquid and liquid) of dairy and meat were soaked together for 24 hours or more, even if cold, they are all not kosher.
Exception In any of these three cases, in which one is less than 1/60th the volume of the other:

• The larger food is kosher.
• The lesser one is non-kosher.

Note You must remove the smaller food from the larger one and wash off the larger one, if possible. If you don't know how long the foods soaked together but it may have been less than 24 hours, you may use the foods.