well, there are two types of pentagrams. one is the right side up and another is the upside down pentagram. I am going to briefly explain them to you.
Right side up- The Pentagram right side up represents the Divine ruling over the world of matter. The 5 points represent the 5 places that Christ was wounded. Traditionally they say that Demons are afraid of it. This is TV and movie stuff. Demons would only laugh at you if you thought you could scare them off with a right side pentagram.
Also the five points represent the 5 elements - Spirit, Fire, Earth, Air, Water.
Upside Down- The upside down pentagram represents the material world ruling and in most common uses, it represents Satan or the world of matter ruling over the Divine or Darkness over Light.
Blessed be :)