We wall shoot in this game all the time, that's why I challenged you to shoot at the wall.
Leveling up refers to the CoD Ranking system. Rank 1 - Rank 55 iin CoD4. You unlock weapons and perks by ranking up. Sometimes you just unlock challenges, and that's just ghey.
GUID is your Global User ID. It is unique to your keycode (your version of CoD) wherever you play from (assuming you are using the same game). It is how virtually every ban in CoD4 is handled.
"?" is a Question Mark.
Hope this helps.