Load the nails into the gun's clip. This is typically done by pulling a spring-loaded bar in the clip downwards, then sliding the nails in from the top. Release the bar when the nails are in.
Attach the power source to the nail gun. Most nail guns are pneumatic, and will require a compressor and air hose for power.
Press the nail gun's muzzle against whatever material you wish to nail. Make sure the muzzle is pressed firmly against the material, otherwise the gun will not fire correctly.
Pull the trigger to fire a nail into the material. Repeat as necessary.