To make your enemies shoot bullets, in their settings, for the "action step 0" set action "shoot straight", give a timer value and for "End of action" set "GoToFirst".
Then you need to make your ennemie's bullets: it's the "Projectile Source" game object. Set it as "monster weapon", give an "acceleration" and "speed", set "Solid Object Reaction" and "Edge Object Reaction" to "DestoyMe". Then in actions, for the "action step 0" check "ignore gravity".
And set the Bounding box. That's all!
Note: if you want to use the action "Shoot at player" for your monster, in your Projectile Source settings, check "ignore main physics" and "ignore gravity" for "action step 1" (this one is used for shoot at player by the engine).