The body of the screen is a list of the hymns currently associated with this occassion.
The "Add" button opens a dialog to select a hymn from a hymn book, and append it to the list.
The "Remove" button removes the selected hymn from the list.
The "Move Up" and "Move Down" buttons move the selected hymn within the list.
The "Help" button, shows this screen.
The "Cancel" button, closes the screen, ignoring any changes.
The "Ok" button, closes the screen, saving any changes.