I am trying to create a save the date invitation. The bride wants the invitations to have rounded edges of about .5 inches. Is this something I can do to the art board itself, or do I just create a rounded edge rectangle, put my art on that, and specify to the printers how to cut the art?
You can’t round an artboard.
You could use a rounded rectangle, but you shouldn’t.
Corner rounding on the printed piece is handled after the piece is printed and when it is being folded and cut.
Design with square edges and don’t do anything to indicate rounded corners. Then tell the printer you want the corners rounded when they print it. (note, this may increase printing costs.)