You will need an A4 (or any other size) paper and scissors.
Put your sheet of paper on a flat surface
Fold in half.
Fold along the sides in quarters.
Unfold and fold in half.
And fold along the sides in quarters.
Pinch along the longer crease.
… and here ….
… and here. Cut also in the same spot above.
It will look like this
Pinch both sides, folding the sides to the center, from below.
Finish the folding and hold.
Flatten all flaps to the part below. The top area should hold the less paper folds.
Fold top to bottom.
Flatten strongly. Ready to use!
Now go write down some cool stuff!