You need: 1 square sheet (15×15cm suggested). Start with the colored side down.
Arrows show movement. Dashed lines show folds.
1Fold in half
Place the square as a diamond. Bring the bottom point up to meet the top point.
2Lower one layer only
The top has two layers. Fold only the front point down to the middle of the bottom edge.
3Crease both sides
Fold each side point up to the top point, then unfold. Keep the small front triangle folded down.
4Tuck in the right tip
Fold the right corner up again. Tuck the raised tip into the pocket behind the front triangle.
5Tuck in the left tip
Fold the left corner up and tuck its tip into the same pocket. Press flat.
6Slip over a page corner
Turn the bookmark to fit a page corner. Draw a face or pattern on the outside if you like.