We practice the line-up first with a serve ball from the trainer and then a normal/attack ball from the trainer.
It is important that there is a change of position, the volleyball technique itself (pass, reception, ... are important but in this exercise it is not important).
When the group has had both it is the next group's turn.
The group that just had the ball goes back into the box and stands at the window,
5 times with nose against the window and then walk to the other side, by then the next group is about ready.