There are a variety of approaches to learning to play music. Music Theory can be very helpful to most in that quest. It is a different way of thinking about music and a way to get at the nuance of it all.
For some, it might get in the way of the feel, but for most, it likely is a good thing to learn about. It is very much the language through which music is logically understood. Here are some links.
musictheory.net – Lessons
Introductory and intermediate music theory lessons, exercises, ear trainers, and calculators.
Music theory – Wikipedia
Music theory is the study of the practices and possibilities of music. The Oxford Companion to Music describes three interrelated uses of the term “music theory”: