I've always been involved in music but it was mostly playing written music in band or improvising on the guitar. never sat down and tried to write music. I understand that music consists of mainly ryhthm, melody, harmony, but I have no idea how to write it. I have questions such as: how do I choose a chord progession? (Besides being lazy and using the 1-4-5) what about 7th chords? I don't really understand chords very well or why we need them in music. except that a chord progession is the skeleton of the song. and once I choose a progression, how do I write melody around that? how do I choose a chord progession when I already have a main riff I like? are there any good books/websites/youtube vids for learning musical theory?