Score a 4 X 12 piece of paper every 4" (so you have three squares.) Fold the middle square in half, adhering the edges of that square together, then punching a slot along the fold with the word window punch to form the pocket for the gift card. Adhere the whole thing to the inside of a 4 1/4" x 4 1/4" square card.
You should try it -- it is too cute!!!