How does the court decide who will serve on a jury?

How does the court decide who will serve on a jury?

When you are called into jury duty, and you report, you receive the summons and the whole jury pool shows up and lets say there are sixty people and they only need twelve people for the case. The attorneys for both sides, the prosecutor and the defense attorney, are going to ask people questions and it may be that you are called in and you are excused from jury duty because they don't think that you fit the qualifications of the people they want. Or again, twelve people have already been chosen before they have a chance to talk to you.