iFile is a great little tool that works just like Explorer (win) or Finder (mac). It let's you browse your root files, rename/edit files and you can also do other stuff with it as well.
As with any file exploring software, first rule of thumb is don't delete *****. Always backup and then do whatever you need to do. Fortunately though, there is a recycle bin/trash bin in iFile as well so in the event that you do delete something, you're still able to recover it.
Best advice would be to just tinker around and get used to finding certain locations of files, i.e. themes, SMS sounds, application folders, etc., and just start there.