He is not colliding with any body
Have you tried making a StaticBody2D underneath the player? Make sure to have a CollisionShape2D as a child of the StaticBody2D node. You'll also need to include a shape in the CollisionShape2D.
Your player has a CollisionShape2D right? I didn't think about it before, but that could also be causing your problem.
I don't know what are the character demo. Can you explain me?
You can find the Kinematic character demo in the demos zip on the Godot engine download page. You can find it on the downloads page if you scroll down a little bit, it's a big white button that reads "Demos. Example projects to get you started". Just download the zip, open the Godot project manager, click "scan", and point it to the extracted zip folder. The demo you want to look at is called "Kinematic Character" and has a picture with some purple squares, a white square, and a pink square.
(On an aside: There is no reason to apologize for being a beginner! Everyone has to start somewhere. :smiley: Helping others is what we're here for! Along with sharing progress, projects, assets, and other stuff :wink: )