I learned how to make this origami box in 4th grade, and I've made hundreds of these since. It is a little more difficult than your average origami project, but the end result makes it worth it!
Step 1: Gather Your Materials
For this, you need 6 square Post-Its. You will need 3 different colors with 2 Post-It’s for each color.
Fold the Post-It in half vertically, then unfold it so there is a line down the center.
Fold each of the two existing halves in half & keep them folded.
Take the top left corner and fold it diagonally so the top edge is now in line with the right edge. Flip the Post-It around and do the same with the other side.
Unfold one of the triangles. Grab the small flap and tuck it behind the paper. Repeat this with the other side.
Fold the triangles that are sticking out of each side of the Post-It back so that it looks like a square with two triangles sticking out on the bottom
Step 7: Repeat
Repeat steps 2-6 five times until you have 6 Post-Its that are all folded the same way.
Step 8: Begin to Assemble
Now you are going to start assembling your cube. You’re going to use 4 of the Post-Its (2 different colors) in this first step. I will be starting with blue and purple. Take two Post-Its of different colors and insert one of the triangles on the blue Post-It into one of the pockets on the purple Post-It. Make sure you’re tucking it into one of the pockets on the side so that it’s not going over another triangle because you will be tucking in all of the triangles somewhere. Tuck a triangle from the other blue Post-It into the opposite side of the purple Post-It. Flip the semi-formed box around and tuck the other blue triangles into the pockets on the other purple Post-It. When you are done with this step, you should have 4 sides of the box formed, with just the top and bottom missing.
Step 9: Finish Assembling
Take one of the pink Post-Its and have it cover either the top or bottom of the cube. Tuck the triangles into the pockets on the blue Post-Its. You should have one triangle tucked into each Post-It. From here, you need to tuck the purple triangles into the corresponding pockets on the pink Post-It. Repeat this process with the other Post-It on the other side of the cube. Now you have yourself an origami Post-It cube!