Choose a fleet. The node runs on it until you change it.

A fleet is a named set of models, with a role for each one, that a node runs on — a root, a child, whatever rungs the deployment needs. You pick one at setup, and you can change it any time, from the console or by telling the node its name. A node can also compose a custom fleet of its own and draft it for your approval; nothing here runs until you say so.