Mix the cleaner or solution with water, or just add straight cleaner if that is what the directions on your foam gun call for, inside the plastic container attached to the bottom of the nozzle. Screw the container to its lid, which is mounted on the underside of the nozzle.
Attach the water hose to the bottom of the spray trigger handle on your foam gun.
Set the multiratio mixing dial to one of the settings appropriate for your job by turning the dial.
Turn the hose on and squeeze the handle trigger to use your foam gun.