A volleyball formation is how players move and position themselves on the court. There are three main formations used:
This is a formation that uses one setter and five hitters. Other than the one setter, every other player is looking to make an attack.
This is a formation that uses four hitters and two setters. The two setters set up attacks in the front court for the hitters to make. There's usually one setter in the front row and one in the back row.
This is a formation with four spikers and two setters. A player from the back row comes up to help the front row hitters to make four. In this formation all players can act as hitters to try to score points, that's where the six comes from.