The R4 media cartridge for Nintendo DS allows users to download and run a host of amateur-developed games and software on the system. In addition to software designed for Nintendo DS, the cartridge can also run games and software developed for Nintendo's previous system, the Game Boy Advance. Running Game Boy Advance software requires an additional memory cartridge such as an EZ-Flash or Nintendo's own DS Memory Expander.
Download the GBA Exploader software from the site in Resources. Double-click the downloaded file to unzip it.
Connect the MicroSD card for your R4 cartridge to your PC's USB port using the R4's MicroSD adaptor. Copy all unzipped Exploader files to the root directory of the card.
Create two directories on your R4's MicroSD card called "GBA" and "GBA_SAVE." Copy your GBA games into the "GBA" directory. Many sites provide amateur-developed and public-domain games for GBA.
Disconnect your MicroSD adaptor and remove the MicroSD card. Insert the card into the R4 cartridge and insert the cartridge into the top slot of your Nintendo DS. Insert a memory-expansion device such as EZ-Flash or Nintendo's DS Memory Expander into the bottom slot and turn the system on.
Select "R4 DS" from the DS' home screen. Choose "GBA Exploader" from the R4 menu.
Scroll to the GBA game you wish to load using the D-pad. Press "A" to load any of the GBA games stored on your R4.
It's illegal to use media cartridges or memory extenders (even Nintendo's own device) to load commercially available software. Only download from sites offering public-domain or "home-brew" software.