One worm per team. Upon starting the game, worm's should be placed on the first shot location. There is usually a numbered sign (1), and a colored line next to it from which the worms should attempt their shots. Any shot outside that area doesn't count. The goal is to throw a nade to the hole labeled like the sign you're standing next to, in order.
THE NADE MUST STAY IN THE HOLE AND EXPLODE INSIDE. IT DOESN'T NEED TO BE TOTALLY STOPPED AS LONG AS IT'S TOUCHING THE GROUND OF THE HOLE.
Once you complete a hole you move to the next one. You're free to use rope/jetpack on your next turn and attempt the next shot on that same turn, if possible.
If there's any doubts please take a look at the maps provided, they will help make things clear.