Kabbalat Shabbat is mostly omitted when Shabbat falls on:

• Jewish festivals,
• Chol ha'moed, and
• Right after the last day of a Jewish festival. 

On these days, only Mizmor shir... and Adonai malach... are said.
 

Kabbalat Shabbat should ideally be started before sunset, and you should ideally get to bo'i challa at about sunset time. But you may start Kabbalat Shabbat after sunset and even after dark.

The latest time to finish saying Kabbalat Shabbat is before daybreak on Saturday morning.

It is not the custom for women to get public consolation (nichum aveilim) on Friday night at synagogue.

For women and public consolation (nichum aveilim), see Women and Public Consolation after Kabbalat Shabbat.

A mourner enters the synagogue on Friday evening before Mizmor shir l'yom haShabbat (after the main part of Kabbalat Shabbat has finished).
Reason Mizmor shir is the actual starting point of Shabbat.
The congregation stands and, as the mourners walk in, greets the mourners with “HaMakom yenacheim etchem b'toch she'ar aveilei tzion v'yrushalayim.

Choose the greatest Jewish scholar (talmid chacham) in your town or city as sandak (person who holds the baby for the brit mila), since kabbala says it is a good omen for the boy's soul. A woman may be a sandeket but only if no suitable man is available.  If no Jewish man or woman is available, a non-Jewish person may serve as a sandak or sandeket.

Before eating bread (at any time, not just on Shabbat or Jewish festivals), the bread should be dipped in some salt. This makes it taste better and makes it like a sacrifice (which had salt added to it).

Before eating bread (at any time, not just on Shabbat or Jewish festivals), dip the bread in some salt.

Yom Kippur is the Day of Atonement. In ancient times, it was more festive than now and unmarried people of both genders would meet and try to find their future spouses.
Yom Kippur is a serious but also a happy day, since all Jews who repent (do teshuva) have their sins forgiven on that day.
Teshuva has four main parts:

• Charata  Regretting what we have done and feeling bad about it.
• Vidui  Recognizing and admitting that we have done something wrong.
•  Kabala  Resolving not to repeat that mistake.
• Azivat hachet  Being in the same situation as before but avoiding doing the sin.

The Torah tells us that there is an inherent property to Yom Kippur that causes spiritual purification and removes sins.
All Jews can become like angels on Yom Kippur.  In order to imitate angels (which are spiritual beings), we abstain from five activities that are associated with physical beings. We do not wash, anoint our bodies, eat or drink, have intimate relations, or wear leather shoes. To further imitate angels, when we say the shema, we say Baruch shem kevod malchuto l'olam va'ed out loud, as opposed to the rest of the year, when we say it quietly.
For more on fast days, see Fast Days.