Very simply put, Feng shui is concerned with humans and nature, and how to best live in harmony within our environments. It all relates to the notion that if we as humans learn to live in balance with nature, we will be happy and prosper. The modern concern for ecology in a way is part of those ideas, as people are learning that what is good for the environment and the earth is also good for humans.
Basic Feng shui equates our surroundings with not only our physical well being, but our mental and spiritual well being as well. They are all connected, and to neglect one is to be out of balance with the others, which does not lead to happiness and prosperity. We can well imagine the frame of mind and our emotional state if we were to be surrounded by a room with no windows and barren walls. Or an environment of death and destruction, or ugliness and hate. These environments would affect us, throw our emotional and spiritual well being out of balance and eventually affect our physical well being. We will become corrupt in body and spirit, which would lead to our environment becoming even more corrupt, and the circle of imbalance continues. But if we balance our environments with things of beauty, music, windows that open to let the fresh air in, sometimes the simplest of things, it is possible to reverse the negative environments to positive and break the circle of imbalance, and lead lives of happiness and prosperity.
Feng shui is often portrayed as something complex, something that only a master of immense training and even psychic abilities can practice. Feng shui, as with all things,can be as complex as you wish to make it. But if Feng shui can be reduced to one word, that word would be balance. Be in balance with your environment. If there is darkness, make some light. If there is ugliness, bring some beauty. This can be done by obeying strict rules and practices of a Feng shui master, to be sure. But it can also be done in a very basic way by anyone. For what brings balance to you and your environment is a very personal thing. Add some beauty, some compassion, some concern for your environment, and you will be repaid. You may not be a master, but you will be practicing the ancient philosophy of balance that is the core idea of Feng shui.