That KidsCanCode video is pretty good and will work on Godot 3.0 (I'm using 3.0.4 Mono).
What in particular didn't work? Did you download their code or type it in yourself?
I recently struggled to get it going also, with a Tilemap, but eventually got there. I'm at work now but if you don't have an answer soon I can post some code.
Edit: Try this tutorial also. It's always good having multiple explanations of the same thing, I find:) You want the first part. The second part goes into A*/AStar, which you might find interesting also.