Being zen is to practice the great sitting of the Buddhas, namely the zazen, sitting meditation in the posture of the lotus, which is the essence of Buddhism.
Through this practice, we become intimate with ourselves. This intimacy drives us to the understanding of our true self. Understanding our true nature allows us to harmonize ourselves and to melt us with the full universe, so to put us in agreement with it and to follow the cosmic order. That brings us not to think that we are so important and to appreciate more the world which surrounds us in discovering it as it is and not deformed by our own ideas.To discover the world the way it is, gives us the choice not to accept blindly the descriptions which are given to us from our birth and gives us the possibility not to be abused by the others or by ourselves. We then have the choice not to let us be dragged in the vicious circles out of which we cannot go until our death.
From that comes a feeling of freedom which push us to believe, but to believe because we have chosen to believe and not by superstition. To believe is then the expression of our free will, it is a creative belief.
Being zen is to know to forget about ourselves and then to be able to concentrate on a single thing. We should know why we do things and then act, without doubt nor regret. Not to doubt is also to balance fear and courage.
Being zen is to know to make the silence inside of ourselves and discover this way our true dimension which then appears, as if the words would have kept it prisoner.
Source: Zen-Deshimaru.com