The pentagram has held many meanings over the centuries. In early Christianity it represented the Five Wounds of Christ. However, in the Western Occult Tradition it is generally used to represent the five Elements of Earth, Air, Fire, Water, and Spirit.
You can find information on the Hexagram at http://altreligion.about.com/od/westernocculttradition/a/The-Hexagram.htm
And here's a link about the Septagram - http://altreligion.about.com/od/symbols/ig/Geometric-Shapes/Heptagram--Acute.htm