There are two primary ways to format games for a JTAG/RGH console:
A complete disc image. These cannot be played directly and must be "extracted" into a folder using tools like Xbox Image Browser GOD (Games on Demand):
Pros: Recognized by the standard Xbox dashboard; faster transfer to internal HDDs because it uses fewer, larger files. Cons: Harder to apply certain file-based mods.
Before you can dive into downloading games, you need to ensure your setup is ready. You cannot simply download a game to a stock console.