And the catch can is just attached to the vent line that is attached to the muffler, when the fuel flows into the catch can it is full and you have lost no fuel at all. A catch can is just something you make up yourself, most of us use an old fuel tank, it has one line with a clunck going to the bottom of the can/tank and one line for a vent with a brass tube holding the two lines together so you can remove them from each other. Iend up emtying mine about every third fly day by plugging it into my pump and running the pump backwards so the fuel in the can goes back into my fuel can.
A question for the OP, can you perhaps find someone to show you how to fill the tank?? Perhaps at a club or flying field?? This is pretty basic and it sounds like you may need someone to show you how to do things like fueling and starting the engine?? Some basic learning may be of great help to you.