First of all you want to make sure your, ummm, I guess that's a hot glue gun? Anyways whatever the fuck that is you want to make sure it's clean and in working order before you even head out. Now as you position yourself by the railing in a crowded mall where no body will notice you and there are of course no witnesses, awkwardly sorta aim your pile of bullshit you call a gun at your target. Don't forget to hold up your other hand and give a thumbs up. Now tightly shut both your eyes and place the scope directly between them.
Alright now take the shot.
This and other useful information can be found in Youngblood #1. Now on sale in a dollar bin near you.