How to make a pathfinding system with grid ("unsolved")

As I said here I did watch a tutorial on “how it works” .
Also looked at this post Pathfinding Algorithm Simulation
Didn’t really check out his data structures, so don’t know about any of that.
If you are experienced with the topic you could help providing some info on how to make a grid for a pathfinding npc so that it walks in that grid.