This is a silencer I made for my Airsoft gun. Made of two toilet paper rolls, one shortened a bit to make it the right length. Wrapped in duct tape, with bits on the rear end to make it stick to the gun (not messy bits all over the place though). Amplifies the sound of a dry fire because it's empty right now, but increases accuracy of shotgun style firing (when you cock the gun multiple times to load more BBs into the chamber). I might put paper in to make it actually silence the gun.
This does not make my gun any quieter (for now anyways). It's just for looks, I guess.
On a real gun, the silencing system is the same. The released gas is moved out the sides of the gun rather than straight out of the barrel creating reduced noise, not complete silence.
Trust me, don't fuss with silencing UNLESS you own an airsoft rifle or an airsoft gun powered by CO2. Trust me, you dont want a stupid looking gun.