Learning music is a very comprehensive term. Learning music can include learning musical instruments, learning to sing, learning to dance, learning to perform, learning harmony, learning music theory, learning chorus, conducting, and sight-singing. But music theory refers to a theory of music. Many people confuse it with physics. It probably talks about the marks on the score and the relationship between various modes. Generally, people who read music will learn music theory and harmony. It can help you get some ideas for composing music. I have finished studying music theory, and now I am studying harmony.