I purchased Rage as a download from Steam. I'm finding the interface frustrating to figure out. Obviously you have to "assign" items to slots, but it is not clear to me how to do this, or how to then USE the items in the slots. Very cumbersome design.
I need some very detailed, explicit, baby-step, take-you-by-the hand information here. Thanks.

If you go to Steam, in the Library, you should have a link to the PDF of the game manual. I am not at my gaming machine, so I can't give you the exact location in Steam. But, I think you get it from a Right Click on the game and the submenu that pops up.

Might want to save it to your HDD, if you can.

Thank you. I already looked there, should have said so. Steam says "Manual: none available".