The drop down list on this field shows the tables which are available to set up Workflow processes for. An entry to the selected table will trigger the Workflow action.
Generally the Workflow is triggered when the record is changed, but in the case of the HR Record, the fields can be monitored too. For example, changes to the next of kin contact information may be of no importance to the HR Department, but changes to the employees address may need to be communicated to the pension company.
Click the button and select the fields to be monitored. The Workflow will be triggered when the content of any of the fields change.