The Body consists aout of various parts
-general proportions
-skeletal landmarks on the human body
-gesture drawing (whole body)
-gesture drawing (hands)
-difference between male/female/kids
-difference between different people of different countries
-portraits
-facial expression
skeleton:
-skull
-spine
-pelvis
-ribcage
-shoulder belt
-arms
-hands
-legs
-feet
all of those parts have their simplified structure, their joints, their muscles, muscle insertion points, fat storages and much more
it's just tons of stuff. Even just nailing down the basics takes a very long time.
Generally there are 2 very important things I'd say every new artist should draw:
1) about 10.000 30 second pose drawings to get some kind of a feeling for the proportion of the human body
2) tons of portraits - because a close up portrait will challenge an artist with all major problems of drawing. You need proportions, simplify your drawing in simple constructive forms, learn each feature for drawing a portrait (skull, nose, eyes, ears, lips) while keeping the stuff in place and respective size.
and because humans are very good at recoginzing other people (unless you suffer from prosopagnosia, but if it's just slight even then it's manageable to draw portraits) - you will instantly see how far you are off from an actual face.
Everything will improve gradually, you will go over one thing let's say skulls, later once you did a few other steps you will get back to it and refine your methods. It's like circles. If you start with it you will also never be "finished", there is always stuff you forget and need to relearn or you might learn a new way how to construct a feature and will get back to that.
Mindless copying references and details and to fully detail won't help you at all... except if you need to copy something. For inventing figures you need to learn how the whole skeleton and all important muscle groups work for certain movements. For learning the stuff crude drawings were you conciously draw each step help a lot more.
Even if it's as "simple" as just making 100 drawings for the size and position relationships for skulls and ribcage and you simplify them just with 2 circles - if you do it consciously and check for each drawing the size relationship, the perspective, the landmarks and then you draw it 100 times you will learn a lot more than you draw 1 fully detailled photorealistic body study.