Hands on experience is the best teacher. See if your area has any clinics nearby that might be geared towards people like yourself. Go to local horse shows (when they restart) of varying disciplines and see what sparks your interest - keep an open mind. Also a good way to meet people and observe how they teach, and of course how their 'product' - their students - seem to enjoy their barn, and of course how the horses are tended to. How do they interact, how are the people working for the trainer treated, from the assistant all the way down to the stall cleaner... are things well managed, running on time, how do they treat their fellow trainers?
There are low stress gigs out there - somewhere around me is a barn that has a weekly thing for low key riders of varying experiences just wanting to be around horses. Visit lots of barns, see their physical barns, their turnout facilities - go in all kinds of weather and see what problems they might have with mud, runoff, snow melt, wind ... shade ... fencing ... and so on, if you're considering having horses on your property. Doing the work of feeding, cleaning, watering, grooming will let you know how you feel about all of it. And for some of us, how much work will our physical selves manage if we plan to do it all. In EVERY season, convenient or not. These things will help you decide how to move forward.
I realize none of these things address books to read - but are no/low cost ways to explore your interest. And ... don't forget the fun of budgeting - because (said with great affection) - board and or feeding/bedding/cleaning is like having a high car payment that never ends, requires expensive manicures every 8 weeks, 2 doctor visits for checkups a year - and at any moment can turn into a giant vet bill. Again, said with great affection.