There are two major forms of energy: Positive energy and negative energy.
Positive energy, also known as masculine or yang, is extroverted and outgoing. It actively reaches out to create new relationships. It goes after what it wants. It is active. The fire signs (Aries, Leo, Sagittarius) and the air signs (Gemini, Libra, Aquarius) belong to the positive polarity.
Negative energy, also known as feminine or yin, is receptive. It does not go after its target. It attempts to attract the target to itself. Femine energy is passive. It wants to sit back and observe. It wants to attract. The earth signs (Taurus, Virgo, Capricorn) and water signs (Cancer, Scorpio, Pisces) belong to the negative polarity.
Some people think that positive signs are better than negative signs, as you would assume the names imply. People also think that masculine energy is stronger than feminine energy. This is not the case. The terms 'yin' and 'yang' more effectively describe this process. Yang (positive, masculine) energy merely reaches out, and yin (negative, feminine) energy merely takes in. No one type is better or stronger than the other. They just have different styles which compliment each other.