<Press the green flag to start> This is a realistic airgun (although it is painted and not a photo). As you maybe know, the airguns must be loaded every single time. So to reload it, press <r>, and, to shoot, press <space>. Oh, press <t> to turn the stage upside down.
Are you me (@crushout) ? If not, shoot 100 times to buy more bullets. Else, press <a> to reload the box with the bullets quickly!