Do you have to reserve a volleyball court or is it first come first serve?

4s courts are reservable and the doubles courts are challenge courts, so winner stays and must accept challenges. When 4s courts are not reserved they are also challenge courts.

Normally, it is informal "First come, first served" pick-up games where winners stay and individual people/groups can challenge winning team for court. The exception to this is during organized league play through the city. If you have further questions just ask someone on a court that is playing at your level.