You do the following with these cards:
1. Cut it out from the mag
2. Place it over the touch screen of your DS
3. Turn the game on (Jump Super Stars)
4. During the game's introduction, trace the line on the card onto your DS's touch screen
5. Start the game. You will get secret special unlockable characters which are S-rank! (don't know what S-rank is, but should be something really powerful).
