There are some really excellent web based resources to help with understanding music theory. My current favourites include:
SIMON BALLE MUSIC THEORY – This link is to our own Simon Balle Music Theory blog which contains lots of links to videos covering all introductory aspects of music theory up to around Grade 5 standard. A good place to start.
TEORIA – this site includes well considered tutorials which will walk you through a topic at your own speed and exercises to test your knowledge.
MUSIC THEORY MINUTE – Dr Jack’s one minute tutorials, useful and concise music theory tutorials.