The term "stop" refers to a type of step that can be incorporated into your automation (a.k.a. drip campaign).
The stop step collects recipients at the end of a workflow branch. Using a stop step allows you to add more to the workflow in the future. Build out the rest of the branch after the Stop, when you're ready to move those recipients forward, remove the Stop. They'll flow to the next step.
Simply drag the Stop element to the desired section of your workflow. There are no more specifications to be entered.