Why learn music theory?
Music theory is the language of music; the mechanics of 'what's going on.' Although theory isn't necessarily an essential part of performing music, it does bring a huge amount of meaning to the sounds we hear and play. With an understanding of theory, music becomes easier to make sense of. It also becomes easier to communicate clearly with other musicians.
Ways of learning music theory
If you have yet to embrace music theory, there is a wealth of information online. Start with 'major scale harmony' and go from there. Alternatively, you can approach music tutors that teach via Skype, enrol in a formal course on learning theory, or if you have a smart phone you can install a music theory app.
How much is enough theory?
How much theory a musician might learn depends on the style of music they perform and their own personal needs. A blues musician may not need much understanding in order to give a good performance. Even in the case of blues though, a little basic knowledge can open doors to new ways of improvising and give the performer new ingredients to add to their musical recipe.
Other benefits of learning theory
Music theory also saves us time. It could take a person hundreds of hours of trial and error improvising in order to stumble on the cool sound of a m7b5 arpeggio played off the 3rd of a dom7 chord. A theory-literate musician however could read this sentence and try it out straight away – as well as many other interesting scale choice options.
Tools of the trade
Music theory also gives composers and songwriters powerful tools. A familiarity of the relationship between notes and chords presents to composer with a variety of musical avenues to go down. Rather than relying on trial and error to find 'that chord' and 'that note,' theory provides an array of candidates for the composer to audition. If a particular chord sequence is not working to the songwriter's satisfaction, he or she can use theory to substitute in alternatives with confidence.
Theory and memory
One final, more subtle, benefit of understanding theory is that music is easier to remember. It is far easier to remember a chord progression or melody when you can see it operating within a familiar framework than when it appears as an anonymous series of chords or notes.
Whatever style of music you are interested in, consider learning some rudimentary theory. Although it can seem a little confusing to the uninitiated, it all makes sense as long as it's presented well. Start simple, put everything in to practice as soon as possible and test yourself regularly. There is nothing to lose from learning the basics and there is plenty to gain!