Well, @NutEllaDraws-lost-count is the resident expert on art tutorials and the like - she has a plethora of helpful videos/links that she can deploy on command like a general. very very cool. Hopefully this should have summoned her. (Generally I'd recommend checking the art discussion board as well for things like this.)
that all being said, anatomy is a Big Oof for me as well - generally, I've heard it's best to start with the bones and then work your way up through muscles and skin. Especially in the beginning, "studying bones" does not equal rendering out beautifully shaded skeletons (though that may be a cool idea as well idk) but looking at the proportions and how things relate to each other. so using sketchy blocks, lines and circles for joints and stuff is encouraged, and you get more technical as you go. this is a pretty helpful introduction to the principle.
(but also, do render out skulls. it's great fun even if it's not supremely helpful)
(and if you're really interested in the actual specific details of the human system, surface googling recommended this site which I think has pretty cool graphics! I could also ask my sister (who's a nurse) for more resources on this if you're interested)
personally, I've found that one of the most important things when it comes to posing is motion. having a super accurate grasp of anatomy is always commendable, but understanding things like balance, lines of action, and weight distribution really help make poses less stiff and more natural. So I'd recommend studying other artists and trying to deconstruct their poses (obviously as personal practice, not to like… spread on the interwebs without credit), as well as referencing photos of people in action (like ballerinas. ballerinas are generally a great study in anatomy and motion.)
I say all this as if I somehow know what I'm doing?? I don't. I have no idea. art is hard. anatomy is hard. drawing an entire image completely without reference sounds like a distant pipe dream
