Resin casting is a bit more expensive to get into because you have to buy supplies constantly, including molds (or mold-making material) and PPE, but it's still cheaper than a lot of other hobbies. It's also easy to make stuff that looks beautiful, even early on the learning curve. After I started posting pictures, friends and family started asking if I could make earrings and such out of the materials I was using. Just finished my fifth and sixth such gifts. Bringing joy to family and friends with something I made myself feels really great. I've also started making phone cases, and I could make some actual money from that on Etsy or similar. And I'm just getting started. There's a near infinite number of techniques I still have yet to learn, so it's likely to keep me amused for quite a while.
In both cases, YouTube videos have been absolutely invaluable. Particularly with the resin casting, I'll see some technique I haven't tried yet, watch several more videos to get different perspectives or explanations, then try it myself. Often I have to go a second round to fix mistakes and improve points of technique that I'd totally missed until I tried it. I try to do at least one pour most days, and to try something new each time unless I'm working on a commission. I literally have a stack of about forty test coasters from working out various techniques, and some of the "failures" showed new effects that I went on to refine. So basically it's practice, practice, practice ... but it's usually practice guided by watching people who have already done stuff.