Clicking it will bring up this dialog:
Here, you will find the list of rules that apply for that user, a checkbox for switching on/off the use of labour rules completely for the user, and the employment date.
The employment date is used for the sabbatical, freeweek and training sub rules. However, by clicking the “Other Dates” button, the dates for these sub rules can be overridden.
You can add rules by right-clicking and choosing “New” or “Add Global Rule”:
If you double-click on a rule you will be able to edit it. Note, however, that this will not affect the global rule that it was originally copied from. This way, you can make adjustments in the rule for one user, without affecting the other users that have the same rule.