^ perhaps a photo would help. But as MA pointed out, it should be wired no differently than a standard CB. The only difference is that there is an added neutral element to help provide additional ground fault protection rather than relying on the full load of the breaker (i.e. 15A, 20A, etc.).
A GFCI will turn the circuit off (interrupt) when there is a current leak. The GFCI monitors the current going to the load (black or “hot” wire) and compares it to the current coming from the load (white, “common” wire). If there is any difference between the two, the GFCI will “interrupt” or turn the circuit off.