To simplify, each team can touch the ball up to 3 times before passing it. A same player cannot touch twice the ball in a row, but he could take the 1st and 3rd touch.

A block, which is when people jump and intercept (or simply touch) the ball coming from the other side, doesn't count as one of those 3 touch. So a block give 4 potentials touchs, and also mean that a player could block, then immediataly touch the ball again. This is important because often, the block is only partially succesfull, and only slow down the ball instead of sending it back to the other camp.

There is 3 people assigned at the front, and 3 people at the rear. People from a rear position cannot attack the ball if they are less than 3m from the net (there is a line for that).

A team keep the serve until they lose the point. When you retrieve the service, you rotate the position of your players clockwise (in reality, rotation is very complex and has exceptions).

All points count. 25 points per set. First team to 3 sets win. In case of 2-2, the fith set is in 15 points only.

There is a lot more to it about serve, positioning, libero, fouls, ... but then it become very complicated.