Oncology? What exactly is that?

I want to be an oncologist, but i'm not exactly sure what it is. Are there different categories to oncology? Like is an oncologist a surgeon or someone who helps patients treat cancer? If there is a difference can you please tell me what the different branches are? Also how many years of school do you need (starting from once you get out of high school)? What is a good school to go to for this major and how much money does an oncologist make? Finally is there a difference between a pediatric oncologist and a regular one (besides the fact that a pediatric oncologist deals with kids)? Thanks so much.