I don't know too much about astrology, but here's a quicky for all you enthusiasts:
Your "sign" as it's referred to, is the sign that the sun was in at the time you were born (sun sign). It represents only the way you appear to others. Below is a brief description of some other important aspects of the chart.
Ascendent: has to be calculated using this great long formula involving latitude and longitude of your place of birth. It represents your true self, or who you will become as time wears on.
Moon: Represents your emotional side, how you deal with feelings and how others percieve your emotional self.
Venus: How you deal with/feel about relationships. This is relationships of all sorts, even just people you run into on the street.
Mars: Drive/motivation. What you want to accomplish and how you'll go about acheiving it.
There's a ton of other stuff to do with placement but my god it'd take years to learn. With the exception of the ascendent the above signs can be determined by looking up your DOB in an ephemeris. I have one in the basement somewhere, so if anyone wants to know some of their other signs, send me a PM with your DOB and I'll go look it up for you.
Of course, I've yet to see solid scientific evidence that this stuff is reliable...all in fun!