I am so in love with these boxes! The box is approximately 3" x 2-1/2" x 2" and it is compatible with both the 8x12 and 12x12 mats. The file comes with the box, the coordinating mats, and the paper elements shown. The box closes in toward the hidden card area and then the hidden card folds down and has a flap that tucks into a slot. When the recipient opens the box, the first thing they will see is your message and then they open the second area to expose the goodies! You can find a full tutorial and additional images on my blog: http://jamielanedesigns.blogspot.com/2014/12/gift-boxes-with-hidden-card.html