Progressions are a mathematical way of moving the planets in your chart. Progressions show the subtle, inner, and psychological influences that influence you as you grow through life experiences.
There are several methods for doing this, but the most common is called Secondary Progressions. Every year, astrologers move your chart forward one day. For example, I was born on July 3, 1968. In 2012, I would have been 44 years old. My progressed chart would be calculated for 44 days more than July 3, for August 16, 1968.
The idea is that you take on different ‘flavors” as you grow older. A person who was born on the first day of Cancer would have a Cancerian influence for the first thirty years of life. During the second thirty years of life, she or he would still be a Cancer. However, she or he would take on a Leo influence. This would flavor the adventurous Leo energy with the pragmatic grounding of Leo. The easiest way to understand these changing influences is to schedule annual updates with a competent astrologer.