Body work questions.

Hey guys. I guess I'm gonna start doing the body work on my car, but had some questions since I've never done this before.
I need to know what grit sand papers I need to work with on this project and I have a pretty bad spot below my driver door that I'm not sure what I'd need to do to get it fixed.
Here are pics of that spot and one of my car.
Thanks for any info.
http://webpages.charter.net/skaterjoe/door1.jpg
http://webpages.charter.net/skaterjoe/door2.jpg
http://webpages.charter.net/skaterjoe/4g4d.jpg

Woah thats sick, how did that happen? looks like it got pushed from the inside... Well you could take off the backing, take one of the body pick hammers, and tap them. If you want to sand down and stuff, then go with 60 or 80 grit first, then hit a 200, then finish it with 400-600 grit. Thats what I always do, never fails on me.