For the middle and top rows each wood piece will get a hole on the end and a second hole on the outside edge of that same end. Note, for the middle and top rows the holes on the ends are to be made diagonally. You can make a diagonal hole with your drill by drilling in at an angle or you can use a kreg jig. Once your bottom row is assembled, continue with the next row. Ronny used 3″ wood screws. The diagonal hole allows you to screw one row onto another.