The Planets' Roles in Astrology
Similarly, Venus rules love and relationships, so its sign tells the astrologer something about how a person reacts to new friends or problems in a marriage. Venus in Scorpio can mean great passion (but also great potential for jealousy); Venus in Aries means a tendency to take the lead in romance.
The planets' relationships to each other are also meaningful; some arrangements cause their influences to increase, while others cause the opposite. To take a very simplistic example, someone who has Venus in opposition (a subtractive arrangement) to Mercury can have trouble communicating about love.
Each planet also rules one or more signs, and when it appears in its sign its influence is magnified. The Moon rules Cancer, so having the Moon in Cancer means that your likelihood of being a nurturing person who cares deeply about feelings is greater.
For a complete list of the planets and their meanings and influences, check an in-depth discussion of Western astrology. That way, the next time someone asks you your sign, you'll realize how much they still don't know about you!