I cut that heart out to serve as a template for the top and bottom of all of my boxes. I traced that heart and flipped it over to trace another one (because the top and bottom will be flipped horizontally from one another). Next, I cut out the hearts for the top and bottom of my box leaving a 1/4 inch border around the outside of the drawn heart. (It doesn't matter that it's exact; it can be a little more or less)
Next, you'll use a scoring tool to score along the line of the drawn heart. Then, using a pair of scissors, you'll notch the border around the heart, with the notches ending at the score line. Fold the notches toward the center of the heart with the drawn side up.
For the top, you will cut a 1 inch strip of paper long enough to go around the whole heart. You want to make sure that when you draw your heart, the circumference is less than 12 inches, so you don't have to glue 2 strips together like I did. One tab at a time, glue the strip to your tabs using a fast drying, liquid glue (like glossy accents).
At this point, you have a plain box that you can decorate any way you like. I made 4: one decorated with patterned paper, and the rest with washi tape.
Our blank Valentines will be 3 x 4 journal cards, so I cut a slit in the top of the box 3.25 inches wide with a craft knife.
It's a little early to set up our love note station, but it will look something like this