The GBA Emulator has a section called cheats. The cheats need to be entered in a specific combination of numbers and letters. You can obtain the the codes through various websites.
You can use the following one to obtain some codes for your games: http://www.neoseeker.com/Games/gameshark_codes/
The codes look like this:
9820F6 AE8203
51F0D8 DF70D1
407403 064659
Entering a wrong cheat code might crash the application.
