I'm not the person who you're replying to, but the number system is very simple to pick up. If you click the book in the bottom right, it explains the mechanics to the game.
The numbers show how much "Monster Power" that square is touching. The example in the book shows a 5 that is touching a Bat (2), a Bat (2), and a Rat (1).
So, this example going left to right, top to bottom