The undo command is an option on the edit menu. It also appears as an icon on the toolbar. This option becomes available when certain modifications to lesson data take place. Otherwise the toolbar button and the menu selection option appear faded (ghosted).
Undo's purpose is to cancel a command that has altered lesson data in a way that is undesirable. For example, picture and sound lessons allow you to restore sound data that was inadvertantly changed or deleted. To execute the undo command, simply click on the undo button.
Many word processors have redo and undo commands. These commands work in a similar way.