To begin with, you should have a clear idea of what you want to be able to do as a musician. Do you want to be able to play an instrument, talk intelligently about music, sing, dance, compose? Specifically what type, style, genre, or tradition of music do you want to be capable in (as an instrumentalist, composer, etc.). Do you have a musical role model, someone who has gained the skills that you would like to master? If you have multiple goals, pick the one that interests you most right now. If you do not have any, choose a goal that you think you might enjoy even if you eventually change goals. (Good musicians typically choose new music-learning goals regularly, so do not be concerned that you might not pick the "right" goal.)
You should have in mind a particular kind of musician, for example a "Celtic-harp player" or a "heavy-metal song-writer" or a "choir tenor." Your question for this inquiry is What kinds of music reading and writing skills do such musicians have, and how might I acquire those skills?