The unavailability function allows you or the employees themselves to set them as unavailable for certain time periods.
You can mark people as unavailable for the days when they are not free to work - the unavailable days will be displayed on the Schedule Calendar in a light grey colour.
To add an unavailability simply right-click on a person's row and choose 'Mark as unavailable'. Next, a window will open where you can enter either a single period unavailability or select multiple days when the person will be unavailable.
Important: If a person is unavailable it won't be possible to assign shifts to them for that period.