Knowing the sign placements of your planets and how they affect you is like have a big pile of auto parts: you could deduce what kind of car they're from, but unless they are all connected up the right way, that pile isn't going to get you very far.
The ways your parts connect to each other are called ASPECTS. The Zodiac, like any other circle, divides up into 360 degrees. We usually don't think of it that way -- we usually think of the Zodiac as being divided into twelve chunks of 30 degrees each. Each 30 degree chunk is called a "sign:" Aries is the first 30 degree chunk; Taurus is the next one, and so on. Whenever one planet approaches a certain number of degrees from another, those two planets are said to be "performing an aspect."
Like a clock, a birth chart is a round thing divided up into 12 slices. The planets travel around the outside of the birth chart/clock face. Earth is considered to be the middle of the clock. (And yes: astrologers do know that the Earth isn't the center of the solar system. We also know the Earth isn't flat. This demonstrates that astrologers have a better scientific grounding than many of astrology's critics. The birth chart, however, assumes that you are the center of your Universe... at least for purposes of doing astrology. If you need proof that you aren't the actual center of the Universe, go stand in line to get your driver's license renewed.)
Now imagine a clock with a planet at the end of each hand. Every hour, on the hour, those two "planets" make an aspect to each other. Each aspect has its own specialized name and qualities that it brings to the table.
Same sign: 0 degrees Conjunction (12 noon)
One Sign away: 30 degrees Semisextile (1 o'clock)
Two Signs away: 60 degrees Sextile (2 o'clock)
Three Signs away: 90 degrees Square (3 o'clock)
Four Signs away: 120 degrees Trine (4 o'clock)
Five Signs away: 150 degrees Quincunx (5 o'clock)
Six Signs away: 180 degrees Opposition (6 o'clock)
If you look at the degree and sign placement of a planet in your birth chart, it won't take long for you to figure out what aspects that planet has to any of the other planets in your chart. The type of aspect is determined by the distance between the two planets. For example, suppose your Venus is at 15 degrees Aries, and let's say your Mars is also at 15 degrees, but not necessarily in the same sign. Because the two planets are at the same number of degrees in their respective signs, we know there is an aspect between the two of them. By looking at the number of signs/degrees these two planets are from each other, we can tell what the aspect is.
These numbers don't have to be exact... in fact, they usually aren't. If Venus is at 15 degrees Aries and Mars is at 12 degrees Aquarius or Gemini, they are still considered to "sextile" each other. The difference in degrees from the exact aspect is what is called "orb." In the example just given, you would therefore say "I have Venus sextile Mars within an orb of two degrees." Once you've figured out that trick and start wandering around telling people things like that... congratulations, you at least sound like you know what you are talking about. And to a certain extent, you probably do.
Most astrologers will allow five or six degrees of orb and still count it as an aspect. If the Sun or Moon are one of the planets involved, most astrologers will allow up to ten degrees of orb. However, the closest an aspect is to "exact" (zero degrees orb), the "stronger" it is considered. And generally, astrologers call the semi-sextile and the quincunx closer than that... more like two or three degrees (a couple more if the Sun and/or Moon are involved). Think of the other aspects in the columns above as "major" aspects, and the semi-sextile and quincunx as "medium" aspects.
(By the way, there are a whole slew of "minor" aspects, with names like "semi-square" and "quintile" and "septile" and such. We'll get to those guys in the next installment.)
Seeing how all these parts connect and how they get along with each other is where a lot of the real excitement and individuality of you and your birth chart come from.
Now, for those of you who have already signed up here at The World's Mightiest Astrology Dating Site, it's time to go grab that free personality profile you got, because next time we'll be looking at how the different aspects affect you, and make you different from anyone else.