To start or stop a campaign that has been created, navigate to the Live Monitoring page on the main navigation bar. Once here, scroll to the campaign you want to start or stop on the left-hand side of the screen.
Once you have the correct campaign selected use the play or pause button in the right-hand corner of the screen. Note that the campaign will enter into a "starting" or "Stopping" phase which will take a few seconds to process. You will notice that when stopped the campaign will turn read and purple when running.
Note that if not manually stopped campaigns will remain running, however regardless your call list will close at midnight automatically and need to be renewed the following day if you wish to continue running. Conversely, you can auto-start and stop your campaign on the campaign creation page.