If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Billy the Kid is a first person shooter game in which you have to shoot on Billy and his acolytes. Those guys are under cover behind multiples part of decors but they are going to show themselves from time to time to aim at you. Shoot at them as soon as possible before they get close enough to reach you. You must also avoid shooting civilians, unless you don’t mind loosing points and lives.