depends what u want it 2 do. if u want it just a normal laser that fires at 1 point, say as a tripwire, get an env_laser and (what i do) get it 2 point at an info_target or any entity. then choose the colour ect. ect. then fire when triiped another entity, like what they did in "we've got hostiles". theres more tuts and example maps on lasers here u can use.