books to understand drawing anatomy?

so i've been creating art my entire life, but recently i've started taking it more seriously because i want to go study art in college. i mostly use charcoal and oil pastels but also colored pencils and watercolor sometimes.

my problem is, i don't know how to draw any kind of body without a reference.

i can recreate it almost perfectly, but i do not understand anatomy in any kind of way so that i can come up with it in my own head. i do not know how to draw bodies at an angle, while sitting, from above or below, i don't even know how to draw a face if it's not front facing or fully in profile.

are there any kind of books or helpful sites that can make me understand how to learn this? i know it's all about practice, i just don't really get where i go first