"The pentagram actually originated in Mesopotamia some four thousand years ago. Then it became, Sumerian and a Egyptain stellar sign. It is the symbol of harmony,health,and mystic powers. It will either trap or repel negative energy."
My source
Mystical Dragon Magick, teachings of the five inner rings
By D.J Conway
As for drawing it, you can basically do it anywhere depending on the spell. In most circles you can draw one representing each element in the air. Each element has a new starting point on the pentacle.
A five pointed star inside a circle is a symbole of pratection if the middle point is pointing up,i think it can be used for binding is the middle point is pointing down,as for an inverted five pointed star without a circle,it can be used as a satanic symbole or as a symbole for different pagan gods(pan for instance).
The pentagram is a symbol which has many meanings; It can mean the 4 elements combined and working with harmony with ones spirit, it can represent the 5 wounds of christ; Crown of the thorns and nails via crucifixian. It can represent man as being the the microcosmic version of the macrocosmic i.e. a smaller version of god with the pentagram being the mans head and arms and legs. Really and truly a symbol is just a glyph what associations you put to it is what gives it power and so whatever you want the symbol to symbolise will in turn be the source of power that symbol offers.
A ritual which incorperates the use of the pentagram is the lesser banishing ritual of the pentagram you may wish to check this out.
Also how you draw a pentagram is important for example the Lesser banishing ritual of the pentagram tells you to draw the banishing earth pentagram.
The pentagram as was stated is very old. Its most understood original meaning was Venus as the morning and evening star. Venus was associated with the Queen of Heaven Astarte also known as Inanna. The Greeks viewed it as Artemis (evening star) and Aphrodite (morning star). Aphrodite particularly, which is why in Rome the goddess was simply named Venus. Her fruit was the apple, which if cut horizontally across the core, also shows a five point star in the center. Coincidence? Probably not.
As time progressed and the symbol was used in european and western magick, the symbol grew in meaning, representing the four elements (plus spirit at the top) and the figure of a man with arms and legs outstretched.
If you want to go even further into the symbolism of the pentagram, you would need to look into pentagons and the number five in general.
You could use it as a protective amulet, as a symbol of Venus (and her associated deities), or as a way to evoke and banish. When each point represents an element, the way it is drawn focuses on banishing or invoking those particular elements respectively away from or into the symbol made. There is also a system of ranks/levels in certain covens which involves the pentagram symbol.
Here is a neat webpage on the subject I just found through google for you about
http://scrivener.circleofthedarkmoon.org/?p=346
this is just an addition to what others are saying-->>in the initiation into hermetics of franz bardon, the five pointed star is a symbol of the mastery of yourself.. knowing that if use it when evoking, you are the master of yourself (microcosm) and no spirit would influence you unless you say so..