Body work, beginning?

[bomber240]

I am ready to start some basic body work prep before going in to get a paint job I've been saving up for but have ZERO experience doing any of this stuff. I had a friend close the hood on the car a few years ago with the oil cap off and resting on top of the valve cover, causing a serious bump in the middle of the hood. I evened out the bump, but need to treat it and several other smaller "minor rust" spots. What should I use for this and where to begin. I also have a few MINOR dings from peoples doors as well I would like to know how to correct? Any help appreciated.

[y3llows14]

Do you guys have any recommendation on sanding the car down for painting. Some people told me to sand down to metal with 40 grits to 80 before priming and some tell me to wet sand with 400 and so forth. Which one will have better result? Thanks.