How do you mod

if you mean modding xbox 360 games you need to download Hex Editor and if your a noob Modio and possibly Halo 3 Toy Box and you need to purchase a data transfer cable from Microsoft (1-800-4MY-XBOX) and order that for I think $14 then buy of amazon.com or something a devise called XSATA.
If its a PS3 Download Hex Editor and get a USB double side cable or a USB flashdrive.