The gun was aimed with the aft facing periscope that you see in the top right-hand corner of the cockpit.
Move your head position around and you can look into it. Of course, the scope doesn't actually show anything at all, as it has not been coded to do so (too hard/ FR killer.. something like that... it has been discussed before).
In game, just do as has already been said.... F3.
Don't fire your guns until you're absolutely ready to, if you hold your fire many people will get careless and assume that you do not know how to use the guns.