For some, astrology is a just a language used to describe the energies that make up the universe. For others, it's the observation of the planets and the patterns of energy they create at any given moment. Modern astrology emerged out of an ancient awareness that we're a microcosm of the universe. "As above, so below," as the saying goes.

Early cultures followed the movements closely, and lived by the seasons, observing the Sun's annual journey through the Zodiac. They saw that those born under the Sun signs had shared traits.
The other cosmic bodies were observed, with the same human curiosity, and search for meaning. This knowledge of cycles and patterns has been used to ponder fate, predict events and even chose a marriage partner. As the search for meaning in the patterns of stars and planets, a system of Astrology is found in every culture and tradition, with some having an unbroken lineage.

What do the movements of the planets have to do with me?
Your birth (or natal) chart is the position of the planets at the moment of your birth. The psychologist Carl Jung wrote that "like vintage years of wine, we have the qualities of the year and of the season in which we are born." Your birth chart reveals built-in gifts and struggles for this lifetime, along with insights about your personality.

What are horoscopes based on?
Most horoscopes are based on the Sun sign, which are the twelve signs of the Zodiac that most people are familiar with. The Sun sign is your basic nature and can be a great starting point for learning about Astrology. If you're curious, try observing people you know to see how whether or not their Sun sign qualities shine through.
Many astrologers come up with predictions based on your Sun sign and where other planets fall in your solar houses. The solar house is created with your Sun in the first house, and following the Zodiac around counter-clockwise around the wheel.

After the Sun sign, what's next in Astrology?
To find out your other planets, you'll need to get your hands on your birth chart. When you know the time you were born, you're able to cast an accurate chart with the rising sign in place on the wheel. (Note: If you don't know your birth time, cast a Noon chart (with 12:00 pm). When you're ready to go deeper, your Moon sign reveals your emotional nature, the intimate side that only a trusted few are able to see
Astrology and Relationships
To investigate a potential love partner, look first at how well the Sun signs traditionally get along. Each of us is a complex blend of all our planets, so add dimension to your astro analysis by looking at the Moon and Rising signs. Venus reveals what kinds of friends and lovers you are attracted to, and what makes you attractive to others. Mars reveals what revs up your mojo, and how you pursue the object of your desire.

The Message of Mercury
Mercury usually follows the Sun closely, and may be in the same sign. This planet and its aspects to other planets in your birth chart shows your unique communication style. It describes the life of the mind, and what gets those wheels turning.

Understanding Astrology
Astrology doesn't make much sense when approached solely through the intellect. There's a lot of synthesis involved, and there's always more to learn. It's a field that's said to have shallow brooks and deep fjords, and my advice is to dip your pinkie toe in -- stick with Sun signs -- and keep going deeper, as your interest grows. Learning about the grouping of the signs by elements (fire, water, air and earth) and qualities (cardinal, fixed and mutable) is a good foundation for futher study.
Source: astrology.about.com