Feng shui yin yang is the theory that creation is made up of opposites, like hot and cold, male and female, day and night to name just a few. In feng shui, the goal is to keep opposites in balance within your dwelling.
For instance you don't want too much light or too much darkness in your space. By keeping things in balance you can form beneficial qi/chi energy. This is due to the balancing of the yin and yang energies.
Each room of a home has different activities and therefore will have need for more of either the yin or yang energy. Case in point, a bedroom is quiet and soft which helps to induce rest and sleep which is yin energy. While a living room or kitchen has lots of activity in it thereby creating a naturally occurring yang energy.
Yin symbolizes the female energy in feng shui yin yang theory. It is also passive, stillness, water, imagination, intuition, creative, soft, quiet, resting, sleeping, meditation, sadness, fatigue, faith, philosophy, traditions, family, respect for nature and beauty, earth.
Items, shapes and colors of yin energy.
Yang symbolizes the male energy in feng shui yin yang theory. It is masculine, hot, sun, sunlight, motion, active, firm, logical, football games, studying, game-playing, analytic, exuberance, aggression, mathematics, finance, reasoning, science, progress, individuals, extracting from nature, heaven.
Items, shapes and colors of yang energy.
The theory of yin and yang is actually common sense in regards to feng shui and how you balance the yin and yang in your space.
If you have a room that is too dark, that is not a good balance of the energies of yin and yang. The room ideally should have a mixture of light and darkness. Not too dark and not too light. Too much darkness could cause levels of depression. Too much light can cause strain. Finding the middle road of the two is the ideal.
A room that is too cold or too hot is not a good balance of the yin and yang energies. When a room is too hot it can cause anger in some people or dry up the sinuses. When a room is too cold, a person, especially children, elderly and people with weak immune systems can get sick. Finding a comfortable middle ground is always the ideal.
Too much noise and activity in a bedroom can interfere with falling asleep, staying asleep and getting a good nights rest. Yet if a living room were very quiet and subdued then a home might not be much fun to live in.
There are more subtle concepts to understanding feng shui yin yang. When it's time for you to add the elements to enliven the energy of the sections of the bagua map, some elements are more yin than yang and vice verse.
Flowing water is yang, while still water is yin. So you wouldn't put flowing water in a bedroom, since a bedroom should be yin for a good nights sleep. If you required the water element in a bedroom, you could use an object in black or dark blue which represents water but without the accompanying yang energy.
Be sure to read the feng shui elements page within this site to better understand feng shui yin yang theory. Then create an awesomely balanced home with beneficial qi/chi energy.
Feng Shui Bagua: The elements that govern feng shui
Feng Shui Cycles: How to balance the five elements
Feng Shui Elements: How to add the elements to your space
Feng Shui Map: The objects, colors and shapes to enliven your space
Feng Shui Yin Yang: Create balance in your home