1. Alright first what you wanna do, is you wanna go to forge.
2. You will see a whole list of versions of forge, press the recommended one not the latest.
3. Now when you have the download file drag that file into your minecraft folder.
4. After that go to your minecraft launcher press the edit profile in the middle it will say new version press on that then go all the way dow the list it will say release 1.6.4-Forge9.11.880 ok then quit the edit profile press play.
5. At the title page it should say at the bottom left a couple of words when it has that quit the game.
6. Go look on google for a mod I suggest the Too Many Items mod. Download that mod.
7. Drag the mod file into your mods folder in your minecraft folder.
8. Open up your minecraft launcher press play, then press mods at the title screen then it will say on the list Too Many Items
9. Go to singleplayer and choose a world, press play
10. And there you have Too Many Items Mod