From what I gathered it's this:
Pulled from HereThe choices are either Live (700 MB required)
or Real (2700 MB required). I have selected the Real Install because I have the space needed for it and it will be able to run faster without the compression. Obviously, if you are using a USB drive or hard drive which is smaller than 2700 MB you won't be able to do the Real Install.
The changes partition is where you can make further changes to your install that normally doesn't happen when you boot... So I understand it. I do not know how to use it, but I know searching around here should give answers. Google around.