Avraham was commanded to circumcise himself and all males in his household. From then on, all healthy Jewish males were to be circumcised when they reached 8 days old.
If there is any question about the baby’s health, the circumcision is delayed or, in rare cases, not done at all.
The primary obligation to do the circumcision is on the boy’s father. Since most people are not skilled surgeons, the actual cutting is usually done by a highly trained expert, called a mohel, who is appointed by the father. A festive meal is eaten after the circumcision.  A minyan is preferred, but not required, for a brit mila.