A worker generates events to record its actions. The events are held in a folder inside the worker and are displayed on the worker screen. You can't view the folder because it automatically redirects back to the worker, but you can view individual event details by clicking on the event timestamp from the worker page, which will show (at a minimum) the timestamp for the event and description of the event.
See Event for a list of event fields.
Events do not automatically track every activity, but are under the control of the process. They show what the process designer thinks would be useful to record and show the user, not everything that is going on.