How are Zen and Buddhism related?
Zen is Buddhism.
Let me put that another way. Zen and Buddhism and the phrase here and now point to to the same thing: the reality of which we are part.
Let me put that yet another way. Zen tradition says that a kind of direct awareness of reality was passed down from the Buddha, through an unbroken lineage of teachers to today’s Zen masters. The term Buddhism encompasses all those who reflect the Buddha’s teaching in the present. Zen is thus a form of Buddhism.