Interval – note relation is the starting point (and the usual basic block that prevents) to play music by understanding what makes music work.
Want to understand scales? Know how to find out any chord from its name? Want to know how songs and their chords are related? Want to talk music?
Here is a set of cards (click to see larger image). Each card shows you the interval name and note relationship for one pitch/key. 12 cards cover all the 12 pitches. Click to download all the cards in one jpg file (5.8MB) (you could print it).
The site has more articles covering the different aspects of intervals and understanding music. More about becoming really good with chords? The Chord Code (with versions)