In between each change in serve, players must rotate positions clockwise. So, if you were serving last, you'd move to zone 6. If you were in zone 5, you'd move up to zone 4, and so on.
When the team receiving the serve scores a point, they then get the chance to serve. Each time the serve switches from team to team, players must rotate. This way, every team member serves.
It all starts with the team that wins the coin toss, they serve first. Once the other team scores a point, they serve. Once the starting team gets the serve again, they must rotate.
If players do not rotate or rotate in the wrong order, the referee will call a rotational fault called overlap
Once the ball is served, players can move from their rotational spot, to the spot they prefer.