I, too, was doing one of those 'OMG' when I read the title...
I don't have much to say about Macs.
I used one, but I'm talking WELL over 15 years ago.
You can start with learning how networking/servers works.
Or, OS' and their integral functions, then programs and how they function -> exploits for the specific OS and/or programs.
Learn programmming languages, start with HTML.
Look at webpages you like and dislike.
If you get into this area I can give you several links.
With the knowledge of language you can do many things to any computer.
What do you want to do first?
You gave a broad spectrum
LBG