Grid System - need a push in the right direciotn

I need to get a grid system build, very similar to what Frank Bignone has done with Pelorea: Total War.

Watch this video

I'll be using squares instead of hexagons, but thats not a big deal. I don't need all the visibility settings and all that extra fancyness. I just need the simple grids drawing and selectable. The problem I am having is I have no clue at all as to where to start to get this going. Any help at all would be greatly appreciated.

Thanks,
Shawn