Score each side at 1 and 10/16- this is perfect when doing milk cartons or one carton and one box. However, if you are doing two boxes side by side it is pretty crowded, so you may want to score at 1 and 12/16 if you are doing 2 boxes (tutorial to follow!)
As you can see in the bottom picture, there is adhesive strips on the outside parts of the second strips. You may want to release some of the backing as it is VERY HARD to do that after the sides go up!
I would suggest that if you are going to stamp right on the paper, to do so now. What I like to do to make my own patterned paper is to mix equal parts fine embossing powder and either fun flock or fine glitter. This adds texture to your paper and is fun as a gift!