In the Configuration tab you indicate the working days of your company. The ticked days are by default available for planning in the scheduling board. For certain actions, such as splitting tickets, only available days are taken into account.
You can set a specific date on unavailable dates in the planning board, for example holidays. Read here how to make a specific day unavailable in the scheduling board.
Through the filter function you can decide whether you want to show or hide unavailable days in the planning board.