I was in the same boat. There are a lot of theory books that will tell you the beginning basics. Best to start with one of these. The one I liked the most was Basic Music Theory by Sol-Ut press. I think it can be found for free - although the free one is not printable. That being said, the thing that has made a huge difference for me was taking a college course - Introduction to Music Theory. If you can take one, maybe at a community college, it will prove invaluable. There is also a great website called Teoria. But I feel that the college course gave me the solid start that I needed. Good luck. You'll get there, it just takes time.