How do I hack gameboy advance roms?

How do I hack gameboy advance roms?

Gameshark?
For PC theres a cheat menu on the top i think under File idk..
Just get the gameshark or action replay code for it=]

I Tryed The PC One But It Fails.

I want to learn how to make my own codes.

You Cant For Roms.Well With Gameshark.