Experiment. A Volca is a really cheap way to start, a minibrute is not much more but considerably more flexible. For ~$400 you could pick up and old Virus A, which is DSP-based but has a great sound all the same, especially in unison mode, and is such a well-specified and designed synth that you'll learn a ton of things that could take you several years to pick up on a piecemeal basis.

Of course software solutions abound but there is no substitute for knob twiddling, and doing it in software makes it too easy to look without really listening.

As far as reading material goes, this is the best course available: https://web.archive.org/web/20160403115835/http://www.soundo...