I have read the Start here, and tools thread. But it seems like looking into too much..

But I just wanted to know a simple answer. Is RIM editing what edits a level or planet or area?

If not, how would I edit a level and create my own planets and locations?

I'm not sure of what you want: there a lot of stuff in the RIMs. If it's a new area you want to create you could start looking at this thread: http://www.lucasforums.com/showthread.php?s=&threadid=122867)

Depends what you mean by "level editing". Could you describe what you want to do?

If this is your first mod, i suggest you start with a small and very definite project.