Practitioners typically sit in lotus or half-lotus position, though chairs are also acceptable. The spine is upright, hands form the cosmic mudra (right hand beneath left, thumbs lightly touching), and eyes remain half-open, gazing downward. Attention rests on the breath, particularly the hara (lower abdomen).
The practice involves "just sitting" (shikantaza)—not trying to achieve any particular state, not pursuing enlightenment, but simply being present with whatever arises. When thoughts appear, practitioners neither suppress nor follow them, but gently return attention to posture and breath.
Zen teachers emphasize that zazen is not a means to enlightenment but enlightenment itself—the practice embodies rather than pursues awakening. Regular zazen develops concentration, cultivates insight into the nature of mind, and manifests in everyday life as mindful presence.
Source
Zen Buddhist Tradition