Well i'm quite new to the linux world also..started messing around with it this spring.
What has really helped me is reading and reading and reading
Start with the Gentoo wiki and the Sabayon wiki, and all the howto's.. and all the forum topics you can muster.
Then you should be a good part on the way...or at least have some headache
PS. Perhaps there should be a howto in the wiki about fixing the missing use flags. DS