I made a version of this card for the most recent card swap (wedding/anniversary) for my scrapbook group. I enjoyed it so much and the technique was pretty fast, so I decided to share it here as a tutorial.
1. Cut a piece of cardstock to 5 1/2" x 12"
2. Score LIGHTLY* at 2", 4", 8" and 10" (I don't have a scoring machine tool thingy, so I used the groove in my paper trimmer and the fatter end of a stylus. It is important to score lightly because the folding may be reversed and you want your card to hold together.)
3. Place cardstock in trimmer at the 1 1/2" mark, with your blade at the 2" mark. Make a slice in the paper from 2" to 10"
4. Flip the cardstock over and make an identical cut on the other side at 1 1/2" from 2" to 10"
5. Fold the top, middle and bottom sections accordion style (basically) as shown below. Note: The front and back of the card are sideways "T" shapes and do not have folds at the middle score. The line will be covered up and enforced by paper.
Here are the folds shown with the card is standing up.
6. Cut paper (I love this Heidi Grace line, so girly) to fit the card in sizes as you wish. And of course... Ink to your delight and adhere to cardstock.
7. Embellish: I used more Heidi Grace paper, Spare Parts lace, Heidi Swapp large brads, and did some stamping and Stickles.
8. Finally, close your Tri-shutter card and just "Try" to give it away. :) You're gonna love it.