Make a right-angled star
Take a square of paper
Fold along the 4 lines of symmetry
In card or stiff paper, cut out a right-angled triangle (a tall skinny one is
good)
Place the triangle on the intersection of the symmetry folds. Rotate it
90o about the right angle.
Rotate this whole shape 45 o about the centre, either by cutting the
whole shape out again in the same or a different colour. (Tissue paper on
a window looks really good)