Tax preparation and consulting has been my primary source of income for most of my adult life, I am professionally licensed and on track to become an owner of my employer, and I have no hesitation when I say I do not know everything about taxes. I'd even say I don't know MOST of the tax law when you consider the various state and local tax laws across the country. With sheer volume of law, court precedence, and regulatory guidance even if you somehow got through it all it would be out of date and incorrect. There is a reason I have to take a minimum of 80 hours of continuing education to maintain my license.
I learned primarily by doing, since my education was not in accounting. Doing forms by hand, doing my own research, learning from coworkers, etc. The H&R Block class might be a good start (I've never taken it), but it is only a start. Given the results I have seen from that "firm", I don't think I'd count on it giving you more than the very basics.