Any astrological interpretation begins with a diagram of the sky erected for the exact time and location of the start of the event in question. When the event is a person's birth, this diagram is called a natal chart or birth chart. To a person trained to read it, this diagram is a describes in broad outlines the journey our spirit has set out upon in this life, as well as the innate tools we brings with us and the potential challenges that we will have to overcome if we wants to achieve fulfillment in life.

Although a natal chart like the one shown below looks quite confusing to a beginner, it's basic design is easy enough to understand with a little help. As mentioned above, the birth chart is a drawing of the sky showing the positions of the planets at the exact time of a person's birth as they appear from the place on Earth where the person was born. Imagine you are standing at the center of the diagram facing South. The eastern horizon is on your left, and the western horizon is on your right. Below this line is the part of the sky that you cannot see:
 

Note: labels are in Bahasa Indonesia; no time yet to redo this diagram.

The sky is divided into twelve sections, called Houses. Because of the rotation of the Earth along its axis, the Sun, Moon and planets appear to rise from the East at the border of House 1 and 12. They then travel through Houses 11, 10, 9, and 8, and set in the West at the border of House 7 and 6. Each house represents a particular area of our lives. An astrologer looks in House 1 to learn about a person's outer personality and appearance, House 2 to find out about money and material possessions, and so on.

Near the outer rim of the wheel are symbols showing the locations of the planets (astrologers include the Sun and Moon in the term "planets" for convenience, even though technically they are not planets). In the diagram above we can see that the Moon has just passed the Midheaven, and Jupiter is to its right. As the time is close to midnight, the symbol for the Sun (a yellow circle with a dot in the middle) is in House 4 at the bottom of the chart near the I.C. (Imum Coeli). The planets in the horoscope symbolize certain drives or needs that everyone has. Mars represents the way we act, Venus represents the way we express love, Mercury the way we think, and so on. You can read more about the drives the planets represent in the lesson on Planetary Symbolism.

The positions of the Sun, Moon, and planets in the houses of the horoscope depends on the daily rotation of the Earth. As mentioned above, this diurnal motion is what makes the planets appear to rise in the East and set in the West. However, the planets are constantly revolving around the Sun, the Moon is revolving around the Earth, and the Earth itself is always going around the Sun—all at different speeds. This means that the positions of the Sun, Moon, and planets as we view them against the background constellations of the galaxy are always changing as well. To measure these movements, astrologers mark the positions of the planets in the Zodiak. This is an imaginary band of sky encircling the Earth whose starting point does not change with respect to the background stars. The zodiak is divided into 12 sections, each 30 degrees wide (12 x 30 deg. = 360 deg. or a perfect circle). These sections are given the names Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagitarius, Capricorn, Aquarius, and Pisces. In the natal chart above, you will see that each planet's position in the zodiak is carefully marked with a special set of symbols.

The signs of the zodiak are like stained-glass windows that modify the basic light of the planets as it passes through them. In this way the signs tell an astrologer how the particular drive represented by a planet will be expressed in an individual's life. For example: Mars represents how we take action, as well as the way we express anger. If Mars is in the zodiacal sign known as Aries, then we will act energetically, spontaneously, and sometimes impulsively. We may blow up easily, but just as quickly forget what made us angry. If, however, Mars is in Scorpio, then we will tend to plan our actions very carefully, and we will be very tenacious in working toward our objectives. We may not get angry easily, but if we do we it will certainly not be easy to forget what offended us. You can read more about the influence of the signs in the lesson on Signs of the Zodiac.

In the middle of the birth chart shown above you will see a confusing mesh of lines with some other strange symbols. These lines and symbols are used to mark planets that are a particular angular distance from each other. The red lines, for instance, show planets that are approximately 120 degrees apart; the green lines connect planets that are about 60 degrees apart. These lines connect planets that always function together. For example, if Mercury (the way we think) is connected to Mars (the way we act), then if we have an idea (Mercury) we will be strongly driven to do something about it (Mars). Our thoughts (Mercury) will also be very active (Mars), and when we get angry with someone (Mars) we will want to say something (Mercury) to him or her. Whether this poses problems for us or not depends on the particular angle between the planets. You can read more about these special angles in the lesson on Aspects.