Cut a square from a piece of paper.

At this point it may be easier to decorate the paper before it is cut and prepared.

Draw lines from corner to corner to mark the cut.

Draw a circle in the centre.

Using scissors cut from each corner into the centre, remembering to stop short at the circle.

Poke a little hole in one corner of each flap, the hole should be just big enough to fit the ink tube through.

Fold each corner with the hole into the centre, then poke the ink fill tube through the whole lot.

Just slip the ink fill back into the pen and it will turn with a slight breeze.