On each of your Dashboards, you will see the current status of your Campaign or Ads. Most common statuses are "Running" and "Paused". Other statuses are:
Running: Ad is running if it can be served.
Paused: Ad is paused by the user, but otherwise capable of being served.
Approved: Ad has been approved and ready to start running.
Pending: Ad is pending approval.
Scheduled: Your ad scheduled to run as soon as it's within your defined Day-parting hours or days.
Stopped: Your campaign has reached the end of it's defined flight dates and will no longer serve.