You download what's called a ROM, and put it on your files, and then click on open (ROM) on your emulator. you can get a ROM from www.coolrom.com
A GBA or NDS, but I think you should use No$gba emulator, it works with both...
Use Google to search for NO$GBA it's an emulator for both DS and GBA games.
easy click cheats and get your cheats
no
emulator-zone.com visualboyadvance is the best.
The best emulator is NO$GBA
One of the best GBA emulators on the market is called No$GBA it is highly ranked. It is advertised to be able to play many types of games on this one emulator.
emulator.com
brothersoft.com
You open and play them in an emulator. The best GBA emulator is Visual Boy Advance. http://vba.ngemu.com/
For the nes, I use: fceux. For game boy color and game boy advance, I use: visual boy advance. for ds games, I use: No$gba. You can get them at: emulator-zone.com
if you mean a gba emulator (gba = gameboy advance ) the best 1 is vba (visual boy advance) and you can get rom's for it on romulation.net