Only way to learn figures is to look at them and draw them. I’ve taken figure drawing and anatomy for artist classes in addition to drawing a lot. Take them if you can! And I fuck up legs more than anything because I don’t draw them enough. Easy springboard though is searching for Andrew Loomis books.
Same with hands, though there are some fairly easy to describe formulas for hands so I drew up a couple rq
First of all, for probably 90% of the hand poses you’re gonna draw, think fingers like the petals on a pinwheel. They all curve the same degree, in relation to the previous.