Holidays and One-Time-Dates are created and managed in the Holidays and One-time Dates Manager, which can be opened using the DATA|holidays menu in the Main Window. This dialog is composed of a TreeView displaying the list of all Holidays Sets on the left, and a tabbed notebook to the right (for more information on the different areas below, click on it).
From within the Holidays Manager, you can: add, delete or modify Holidays Sets directly from within this window, using the toolbar buttons at the top of the TreeView, and you can also use drag and drop to move sets around in the hierarchy.
The 2 tabs to the right allow you to edit the list of recurring holidays and one-time dates. Using the first tab on the right you can add, delete or modify Recurring Holidays and using the second tab you can add, delete or modify One-Time-Dates.