An astrology chart is basically a birth chart that captures the precise astronomical positions of the stars and planets at your birth moment. Using the vast amounts of information provided by your birth chart (or any other astrology charts), astrologers can predict every important event and possible opportunity that can arise in your life.
Around the outside of a birth chart above within twelve segments (see graphic below) are the twelve astrological sun signs (zodiac signs) in sequence. This is a portrayal which the planets are seen to pass through in the sky when viewed from Earth.
In an inner circle is marked all the planets (mercury, etc.) in our solar system (including the sun and the moon), they are portrayed relative to the zodiac.
In the center of the chart their are some marks. These lines indicate a certain relationship to each of the zodiac signs and planets. There various individual interpretations are blended to form the unique character of the individual or event.
There are further important points in your chart, such as the mid-heaven, and sign placement of the moon. Basically, you will be a mixture of the characteristics common to these signs. However, this is far from the whole story. There are many other factors to consider, such as the sign positions of all the other planets, the angular relationships between them and their positions within the astrological houses.
All of this and much, much more, has to be carefully considered in the construction of your birth chart.