Go to your library and find just about any of John Holt's books, also look for The Unschooling Handbook, or The Teenage Liberation Handbook. I know there are many other great reads, but those are my faves up til now.
Unschooling is basically child-led learning. It's using that inborn natural curiosity and love of learning that we're all born with. When one goes to a traditional school (be it public or private) we tend to lose that love or desire of learning.
College and unschooling fit so nicely together, if the person wishes them to. If an unschooled person is at college age and interested in doing something that requires college specialized classes, then that person can and will succeed very well b/c they want to be there (unlike most of the kids there, that are not happy to be there) and want to learn. Unschoolers tend to have a much broader view on our world than trad. schooled kids, so they can also feel confident enough to explore other arenas than college, like traveling, apprenticing at a craft or trade, etc.
go through the MDC archives on this forum, and you're bound to find answers to all your questions and concerns with unschooling