Here's how it's done.
Start with a quarter sheet of origami paper. Full-size hearts are rather large and don't string together well. So simply cut origami paper of your desired color scheme into quarters.
To make a heart:
Fold the square diagonally to create a triangle. Make sure the color side faces out.
Next, fold both side corners to the top tip and crease.
Flip the diamond over and fold the top 2 layers of paper (before you hit the creased paper) down so that the top tip meets the bottom tip. It kind of looks like a mini sailboat at this point.
To make the heart shape, fold the top tips in on themselves. This is going to create the two humps of the heart. Align the crease of the tip with the fold on the backside. When the tip is aligned and folded in on itself, crease.
To finish your heart, simply fold back the very tips and sides to round it off a bit. And you're done!
Make a bunch of the hearts in any color you want. This part makes me super happy. I used 45 hearts on my garland, but the amount you make is up to how long you want your garland to be and how much origami paper you have.
To make the garland, you're going to need some string/thread/ribbon/wire/twine/etc (I used silk cording I found in the beading section at Michael's), something with a sharp point to poke holes (I used my rotary cutter because I'm a college kid), and some clear nail polish.
Here's the deal with the nail polish: It's a super helpful trick for this project. Coat the end of your string with it and let it dry before you start stringing your hearts together. If you don't the string will quickly start to fray at the end and it will become nearly impossible to do all your threading.
To make the hearts into a garland, poke 2 small holes in the middle of each side of the heart. Make sure your pokes are symmetrical.
Then, all you need to do is thread the string through from the back on one side, and then string it back through from the front in the other hole. Make sure you keep consistent which side you string from the back.
If you want, you can knot the string at the front of the holes to keep the hearts in place, but this takes forever so I didn't do it.
Tip: This project gets tangled SUPER easily, so start with that in mind.
Once all your hearts are strung together, you're done! Hang it somewhere where it will be well admired. This garland makes a great party decoration, Valentine's Day festive touch, or a simple bit of happiness to add to your room or office.