I'm self-taught. My grandmother was a seamstress, but she refsed to teach me because she tought I wasn't suited for sewing and wouldn't let me use her machine
I've relied heavily on sewing forums, youtube tutorials, a couple of very good books (clear pictures are essential) and a lot
of practice and patience. Having some knowledge of hand sewing is useful, since some things will require them.
If you want to try your hand at patternmaking, I strongly advise to find a teacher/course.
If you'd like to know a couple of good books for general notion and/or with project suited for beginners, I'll be very glad to provide the titles