Within the Four Pillars, the month (本月 běn​yuè​) that you are born is the pillar that represents information about the person's parents or later years in life. Many Chinese astrologers consider the month pillar to be the most important pillar in determining the circumstances of one's adult life.

The Gregorian (Western) calendar is used for day to day activities in most of East Asia, but the Chinese calendar is still used for marking traditional East Asian holidays such as the Chinese New Year (or Spring Festival (春節).
Solar Terms (节气 jiéqi) are based on seasonal markers and make up the Chinese agricultural calendar. This table shows the correlation between the Western calendar and the Chinese months. It also shows which animals (mnemonic) belong to each astrological month giving the second of the four pillars in Chinese astrology and fortune telling.

I had trouble making this table in html, but if you click the image, you can download the pdf with the full table.