how can i draw a perfect star?

Constructing a hexagram (Star of David) is easy if you have a drawing compass and something with a straight edge. (A tack, string, and pencil can substitute for the compass.) Use these directions to make a hexagon, then extend the sides until they meet.

A pentagram is a bit more tricky. It can be constructed with compass and straightedge. But your best bet might be to use the above method to create five equilateral triangles, cut them out, tape them into a cup shape, and trace the resulting pentagon.