newbie, questions about operating systems and windows 7?

[BrightEyes]

im a newbie at Computers. I am hoping to learn a lot about them this. what is the difference between operating systems and windows 7 or windows explorer? isn't XP and linux kind of the same but windows 7 is more advance? whats the difference between MAC, etc. it seem sI have a lot to learn but I do not know where to start. windows 7? if the new windows 8 comes out will I know basically what to do because I learned windows 7? is the operating system have sub directories. see I don't know where to tart but i hear all this terminology. anybody have any recommendations on how I can learn all this stuff and where to start?
is desktop applications the same hting as operating systems?