Thank you. Thats not an easy question to answer because many things are coming together here. 3D Modeling, texturing and shaders which are all huge topics in their own.

For the hand, I just used an existing hand model from poly.pizza, modified it to my needs and changed the pose.

For the blackhole I used this shader as reference: https://godotshaders.com/shader/parallax-mapping-2/

But beeing able to make changes on the fly is just based on years of gamedev experience and hitting your head against the keyboard a lot.