The employee form fields allow you to define your own individual input fields for the employee section. This way you can capture additional information about your employees, that are individually important to you. For example "date of joining the company", "reliability" or "special skills".
In order to create an employee field go to "account" -> "settings" -> "employee fields":
Here you click on "+add field" and enter the desired title:
The employee fields will now be shown in the employees profiles. They are only visible to admins and managers.