Cheek Piece
You will connect one 1-by-1 black round brick to the megaphone. Place the 1-by-2 black plate piece horizontally on the back of the megaphone piece. The 1-by-2 plate should connect to the megaphone from the back side not on the stud side.
Range Finder Scope Piece
Now you can connect a black 1-by-1 round brick on the black 1-by-2 plate. The black 1-by-1 round brick should now sit at the side of the megaphone piece. You can now connect the transparent white 1-by-1 round plate on the stud on the back of the 1-by-2 plate that is sitting behind the black 1-by-1 round brick piece.
Bi-pod
You now can create the antennas that are positioned below the gun. You should add the black lamp holder on the other stud on the black 1-by-2 plate. The black lamp holder should sit behind the megaphone. On both sides of the black lamp holder, you can connect a black mini-antenna, totaling two antennas.
Target Barrel
Finally, on the stud part of the black lamp holder, connect the black 1-by-1 nose-cone. You will stick in the black light sword-blade into the black 1-by-1 nose-cone and then connect a black 1-by-1 round brick on the nose of the black light sword-blade to complete your Lego mini-gun.