I never heard of the HK-62. As far as how it works, I imagine that you load a full magazine into the little hole on the bottom of the weapon, pull the cocking lever all the way to the rear, let it slide forward under it's own tension, put your finger on the trigger (behind the magazine usually, but it depends on the gun), and pull back on the trigger to fire a shot. You can then repeat the process of pulling the trigger back until you get the desired results.

j/k
Seriously though, can you be more specific in the question? Are you talking about switching fire modes/switching weapons/using the 40mm launcher attachment?