It all depends on the model. I suggest the you contact an air gun repair shop to have it fixed. Try looking up "Air gun repair" on the web and have them repair it for you.
Loading one depends on the model. To fire a BB gun, you pull the trigger.
Not economically feasible.
If its a gun. You pull the trigger while aiming down the sights
Stock or Grip, Hammer, Trigger, Breech, Rail, Barrel, Sights, BB and power source.
Leave it to a trained professional
Trigger, cocking lever, Spring, Piston tube around the spring. BB loder and barrel
You need to state the model and what is wrong with it.
Send it back to the manufacture or contact the manufacture to find out who repairs your BB gun.
The same as a C02 BB gun. When you pull the trigger it momentarily opens a valve to let gas fire the BB down the barrel.
As far as I know Gamo never made a bb gun named the FIX. They did make a model named the CFX, but it is a rifle and shoots pellets, it's not a bb gun. I suggest you contact Gamo at the link below and ask them.
Take the bb gun apart, memorize or take a pic of the inside, find the jam ,and put it back togethor
The Spring is the power source for the gun. When the gun is cocked the spring compresses and when the trigger is pulled the spring releases and pushes a piston that compresses a tube fill of air that fires a BB out of the barrel.