User blog:Tortoiseshel/I'd really like to learn to write music. How would I go about that?

I've been a part of the Vocaloid fandom for about 5 years, and the one of the biggest things that drew me to it was how just about everything is user-generated. And I've always wanted to make my own songs with it, but not only do I have no idea how to compose music, I have no idea what I'd even need to learn. Like, music theory? Chord progession?? Harmony??? What do these words mean?!? Can someone direct me to a site or a book or something where I could learn about this stuff and possibly how to make my own music?