A run is the instance of a workflow. It is a record of each input, trigger, node, result, and output for that instance of the workflow.
Since a run is a particular instance of a workflow, there are several ways to find it. All of these start in the Run console, which you get to by opening the workflow/Task window and selecting the Activity tab and then the Runs menu option:
This tab shows a list of the runs, most recent first. If working with testing, it is possible, you can just look for the name of the workflow you want among those recent runs. However, over to the left of the run screen is a set of options to filter this listing:
You will notice that this does not default to unfiltered, but instead defaults to showing you tree runs (filtering out routines). You can update these filters so that they combine to give you a filter that will help you fine the run you are looking for. Note that Create trees and routines will not have a submission id.