A Job is created when you run a Data Flow. A Job tracks the run-time evidence of that Data Flow and any other processes or Data Flows that run as a consequence of that first Data Flow running. Thus, the Job allows you to track CIC integrations from end to end, for example, from a partner to your back-end system.
The Activity > Jobs screen shows a list of all Jobs run in Express and allows you to filter the list down to the Jobs you are interested in. You can also drill into any Job to get more details. In the Job Detail view, if the Job failed, you can see where and why it failed. Additionally, you can click on each step of the Job to view payloads that were present and log activity that occurred at each step.
For more information, see Working with Jobs.