Hi Heidi, I have assumed you may live in America and so have looked up some info with that in mind, also of course I do not know your personal level of understanding and so forgive me if this info is "To" basic for you.
Here are some sites to Visit and also there is "Music Theory for Dummies available" I'm not infering your a dummy, the fact you want to learn more would deny that.
http://www.berkleemusic.com/welcome/free-music-theory-
lesson?pid=2245&keyword=music-theory&gclid=CMbe5fvD-
5sCFQ9Jagod8xsdAA
http://www.musictheory.net/
http://neilhawes.com/sstheory/theory.htm
http://www.dummies.com/store/product/Music-Theory-For-
Dummies.productCd-0764578383.html
Happy studying.
Fenderphil