KidsCanCode has a tutorial on RigidBody2d Nodes that might be helpful. It was created before Godot 3.0 was released, but most of the concepts and material covered should still apply.
GamesFromScratch has a video tutorial series on 2D physics using Godot 3. I have not watched it myself, but the tutorials from GamesFromScratch are pretty good, I've watched GamesFromScratch tutorials for other topics and found them helpful.