I have fallout 3 on my xbox 360 and i downloaded the G.E.C.K. online but i don't know how to get it on my xbox 360 or if you even can. could you please tell how or if you can thank you

The Geck is strictly for the PC version of the game. You cannot make/use mods on a console.

Like pkleiss said, its only for the PC version. Modding X-Box/Ps3 breaks the EULA, and several other contracts you agree too when playing/buying/using one. So its not allowed. If you want to mod Fo3, buy it for PC. (Which is completely worth it if your computer can run the game)