Fedora startup

Hi
I have recently loaded fedora desktop and another version for testing 
and they run from CD.
At startup they give me option of three startups numbered 1,2 & 3 but 
they donot give the meaning of each startup. Each number is blank.
I have determine 1 runs from the CD, but what do 2 & 3 do?
Cheers
Barry Dean
[e-mail]