Hi, Zizka, I hope you are practicing with shapes.
I do these the same way I would do a drawing with pencil and paper. Learn the shapes of the body. Each part represented by a shape. I wouldn't recommend learning anatomy throught pixelart, though. Making pixelart involves knowing WHAT not to include in the pixelart, that is present in the real object, but it's too small or is too complext for the image resolution.
There are mediums for learning anatomy: book, youtube videos, photo references. Some are specific for drawing some not. For example, I have digital books of medical anatomy, and they are great when I want great detail about a specific region of the body. Books/magazines/tutorials specific for drawing are good too, expecially for beginners (like your case).
Keep going with the practicise and let us updated!