PacMan IA of ghost using nodes/waypoints

I am studying old game programming that will be used in my final exam of the course of games, but I have difficulty understanding how I can make the ghosts move randomly through the labyrinth through nodes / waypoints (this is the first time I work with nodes / waypoints so I do not know how to program and if they are the same thing).

Thank you from anyone who can help, I researched and saw several videos teaching to program the AI ​​of the ghosts, but none worked with me.

My most recent attempt was to follow the "The Weekly Coder" video tutorials video "How to make a game like Pac-Man in Unity 5 - Part 4 - Moving Node to Node" I followed the tutorial since the first part of it, but at the time of testing the unity of the error in this line of video

(

if (o.name! = "Pacman")

         {

             board [(int) pos.x, (int) pos.y] = o;

         }

)

The error says "Array index is out of range"

Thanks to all who can help !!