Cock.

Using the included screwdriver, unscrew the screw on top of the cylinder.

Place the cartridges into the cylinder so that the pins align with their designated slots.

Reinstall the cylinder by carefully tighten the screw with the screwdriver.

Slide the small semicircular lever on the opposite side from the hammer. This is the trigger.

Kindly watch the video of the Ring gun in action:

Be sure before use to read the safety rules here.