How old is the rifle, Is it spring powered, or C02 powered or PCP. If you don't know what you are doing you can damage it more. I would look up on the net under "Air Gun repair" and have a professional repair it if it is not under warrenty.
It is a pistol that fires BBs or Pellets that are powered by Air or C02, NOT Gunpowder. Some countries consider them Firearms some do not consider them firearms.
An air gun is usually a replica of a real firearm that is powered by air or C02 that is used to fire a projectile (Pellet or BB). Only air or C02 is used in the air gun. Whereas a firearm uses gunpowder to fire a bullet. Air guns are powerful but not a powerful as a real firearm.
As soon as you release the pressure on the C02 it will loose all it's gas and will then not be able to fire the gun anymore. You must put in a new C02 powerlett to charge the gun again. The old C02 powerlett can be trashed it can not be recharged.
See the link below.
It is a system that uses C02 or green gas to fire the BB out of the gun
See the link below for the UK air gun laws. Sportsmarketing in Essex sells C02 air guns
When the C02 cylinder is placed into the gun and screwed in the end of the cylinder is pierced and some C02 charges the system of the pistol. When the trigger is pulled a burst of the C02 gas is released behind the pellet, firing it down the barrel. You can usually get about 40 to 50 shots from as regular 12 oz C02 cylinder.
The tank is probably empty, your safety is on, or you have not cocked the gun.
Use C02 to propell the pellet
It works the same as a .22 except if you get hit it hurts more
you screw the adapter into the gun, and then the co2 cartridge.