Re: Trying to grasp the rule.....
If you want to learn theory for college or whatever, then studying books etc is a good way to go. But by far the best way to become a better musician all around is to join a band of some sort. I see it a very similar way to a learning a new language. Where taking lessons in Spanish (for example) is good, it is nothing compared to going to Spain and experiencing the various dialects etc of that language and being thrown in at the deep end so to speak.
So what I'm saying to you is, unless your doing this as a written exam, join a band (but try to join a band of musicians who are more able than yourself so you don't end up the only one who knows any music theory). If you join the right band, it really will help you.