Apart from the following exceptions, all the normal rules governing shooting in Warhammer apply:

During your force's Shooting phase each of your warriors may shoot once with one of his weapons. This means that he can fire a bow, shoot with a crossbow, or hurl a throwing knife, for example.

Work through the models one at a time. Pick which warrior is going to shoot, nominate his target, work out whether he hits the enemy and, if he does, any wounds or injuries that are caused. Then continue with the next shooter. You can take shots in any order you wish. Be sure to remember or note down which models have already shot.