Disclaimer: There is more than one path one can follow in Zen Buddhism. I have made a concerted effort to make this writeup as general as possible. I am a member of Diamond Sangha, and would be interested in messages from members of different sanghas if they have corrections.
What is zen? While the question may seem simple, there is no simple answer. Zen is zen. Perhaps a better way is to explain what zen practice entails, and its goals.
Zazen is the foundation of all zen practice. It is an ongoing process of learning how to be here, now. Zazen is essentially zen meditation, although some are reticent to use this term.
One begins in zazen with breath counting. In and out, in and out. Count ten exhales, or inhales, or one count for each if you need a ramp-up. This sounds simple, but it is not. Your mind is filled with busy things, always flitting to this or that, and this makes extended focus difficult. The practice of zazen is an attempt to control what some call the "monkey mind", and to make your thoughts as clean as a blank piece of paper.
The main point of zazen is to not to beat down and destroy the ego, but to merely control it. If you are like most people, your thoughts constantly invade your mind, this way and that, and it is nearly impossible to give your truly undivided attention to anything. Zazen begins as the difficult path of training your mind to behave itself.
Koans are parables which are given to the student of zen to solve. This is usually after one is able to tame their mind, so that they can work at the problem with their entire mind. In general, it is very difficult to practice zen without a teacher, since you will not know with certainty if you are making progress on your koans without one. That is, of course, unless you reach satori.
Satori is a goal of zen practice. For many it is the ultimate goal. It is the moment of enlightenment in which all is made clear and your relation to the Dharma becomes apparent. It apparently happens to different people at different times for any number of reasons. The goal of the koans is to move your mind in the correct direction for satori. Many have said it is like a thunderbolt, and they go half-mad with joy afterward. I have no first-hand experience with satori yet, so I'll let you know when I get there. One Zen Master said that practice truly begins with satori. You have seen the light, but it is all fuzzy and distant, and that you need to continue to practice until it is crystal clear. He likened it to looking at a tree from 200 yards away. You can tell it's a tree, but you cannot make out its features. However, When you stand directly beneath it you can make out every detail of branches and leaves.
Some say that zen is the purest form of Buddhism, since it involves seeking enlightenment in the same manner in which the Buddha found it. There are no intermediaries, just you and the Dharma.
That being said, there are some important differences between Zen Buddhism and many other forms of zen that are practiced. In Zen Buddhism we not only strive to become Boddhisattva, but we follow the teachings of the Buddha as well.
The Three Treasures are the Buddha, the Dharma and the Sangha. These are the central aspects of Buddhism, and the most important things to a Zen Buddhist.
The Three Refuges are important to Zen Buddhists, but are seemingly more the foundation of other sects of Buddhism, such as is practiced in Tibet. They are as follows:
I take refuge in the Buddha;
I take refuge in the Dharma;
I take refuge in the Sangha.
I will merely summarize here, as a broad treatment belongs in a node of its own.
- No killing.
- No stealing.
- No misuse of sex.
- No lying.
- No dealing in drugs.
- No speaking of faults of others.
- No praising yourself while abusing others.
- No sparing of Dharma assets.
- No indulgence in anger.
- No slandering of the Three Treasures.
There is so much more to zen that I cannot begin to fit it into the scope of one writeup. A short parable summarizes this:
A student of zen once went to his master and said, "Please show me zen."
The master replied, "I must go relieve myself," and left.
Upon his return the master said, "Zen is like going to the bathroom. I cannot go for you. You have to go for yourself."
For the interested in learning more, there are a couple of books I would recommend: