They start with a scribble of random lines. Then you create a creature out of them. I am no pro at this. These are crude and beginning sketches that need to be refined. I might refine them or continue to practice his exercise. It is really fun and I implore you to try it if you like concept art.
I ask to not refine them, these are great for evolution benchmarks, this is today, a couple months in and you can compare how far your art changed, moved, grew (👁 ͜ʖ👁)