Music can be enjoyed by ear, but understanding it brings another joy. Music theory books and composer studies serve students and listeners. Visit music, theatre and film, which includes graded theory papers.
Listening carefully is as important as reading, so keep your instrument or music player nearby and try out each idea as you meet it.
Many arts students build a personal library slowly over the years. Begin with a good general history, add books on your own special interest, and visit performances and galleries as often as you can.
The arts train both the eye and the ear. Whether you are a student or just an admirer, regular practice and careful attention will teach you more than any single theory, though good books certainly guide the way.