A Zen saying says that if you told a fish that the water he swims in is part hydrogen part oxygen, the fish would die of laughter.
When asked the question, "what is Zen about?" I like to tell the story of the Millipede.
The Millipede is an insect with 750 legs (not exactly a thousand, but close!) It can walk and climb leaves with grace and ease. You would say, well, that's not that impressive, I mean ok, it has a lot of legs, but that is his nature, this is how he is composed, that is who the Millipede is. But the saying goes that if you were to ask the Millipede what foot he puts forward first, he would die of confusion.
The point of these small stories is to remind you of something fundamental: we humans tend to ask questions and think more than we experience. I am not suggesting that it is not important to know that water is part hydrogen and part oxygen; I am just saying that sometimes, more often than not, the only essential thing is to have a nice relaxing swim. The way I see Zen training is a way to trust your instincts and your feelings more than your thoughts. Thoughts can often trick you - it is the very nature of our imagination to do so. Your instincts are much harder to fool - but of course, you need to get back in touch with them.
And so, what is Zen? For the Millipede, the answer is simple: putting one foot in front of the other effortlessly, without ever having to think about it.