What is 'the zodiac'?
The zodiac is actually the backdrop to the Sun's apparent pathway through the sky. This pathway is divided into sections that we know as the various zodiac signs. Because the Sun's (apparent) pathway through the heavens is basically constant and can be found at roughly the same spot for the same date in each year, this is how we came to use Sun Signs: the position of the Sun in relation to the backdrop of the zodiac constellations.
This system is convenient because the average person doesn't have to have complicated planetary positions worked out to know which constellation affects them personally, the date of birth is all that is needed in most cases.
All the other planets follow roughly the same path as the Sun, within the zodiac backdrop.
What is a Rising Sign or Ascendant?
The Rising Sign is literally the zodiac sign that is rising on the eastern horizon at the time of birth. This is why the time of birth is important, because without it the Rising Sign cannot be calculated.
What does it mean when a planet is in a sign, i.e., Moon in Aries?
As the planets continue their orbit around the Sun, here on earth their pathway seems to follow the Sun. As they do so, like the Sun they have the zodiac signs as a backdrop behind them. So when an astrologer says that the Moon is in Aries or Mercury is in Virgo this simply means that at a particular time that planet had that particular zodiac sign as it's backdrop.
I am born on a cusp, what does this mean?
When a planet is about to move from one zodiac sign to another along the backdrop it is moving on, this is know as being on the cusp , which causes confusion for most people about which Sun Sign they are (most people are not aware of the positions of the other planets so they are not usually a concern). If you have your time of birth, you can find out exactly which Sun Sign you are using the services of an astrologer or one of the free chart drawing services via the internet.
What is a 'house'?
A birth chart looks a bit like a pie cut into 12 slices. Each of these 'slices' is called a 'house' and can represent various aspects of your life and psychological makeup (depending on the type of interpretation being applied to it). For example, some of the interpretations that can be applied to your second house include: earning capacity, self esteem, values, possessions, 'what I own is what I am', and/or your ability to handle finances.
Why are interpretations by various astrologers so different for the same forecast period?
Just like anybody that you seek advice from, astrologers have different opinions and ways of interpreting the symbolism represented by the planets. The astrologer's training, life experience, and specialisation (ie medical, psychological, spiritual astrology, etc) will all have an effect on the way interpretations are given. I think that it is important to find an astrologer that you feel rapport with because the more open you are, the more you will gain from a personalised forecast.
My friend and I are the same Sun Sign, why are we so different?
When preparing a personalised chart the position of the all the planets are used in determining the psychological makeup of an individual, along with the Sun. The individual planets move at different speeds and will be at various parts of the zodiac backdrop as time moves on. So even if two people are born on the same date with the Sun in the same position, the other planets won't be in the same position. This is important because the position of these other planets will change the interpretation of the birth chart as well as the personalised forecasts.