To do Zen we must have a teacher. To sit quiet & still under a tree & enjoy the life this practice brings, however, only requires being a sincere human being. To do Zen as a sect of Buddhism requires an in person teacher. But to begin meditation in the Zen style does not.
Doing Zen is instantaneous... to sit, we just sit. Zen style meditation is not difficult. But it does require complete honesty with ourselves... willingness to be this honest... sometimes takes practice.

Sitting quiet and still is always the first step.

Regular daily practice of sitting quiet and still, if we allow it to, will infuse itself into our daily lives.

So that we are sitting still, but still acting in our daily lives as well.

We call this doing without doing.