How to Make a Box Out of a Card

From Sherri Osborn, former About.com Guide

Lay both the front and the back of the greeting card on your table with the side that was the inside of the greeting card facing up.

Line up the ruler along one of the short edges and mark the card 3/4" from each corner. Repeat this on the other short side.

Now line up the ruler along one of the long edges, mark the card 3/4" from each corner, and then make another mark 3/4" in from there. Repeat this for the other long side.