In order to set security rights you must be logged in as a supervisor.
By going to any window and pressing Ctrl-F8, you will get the Set Access window. This window will have a list of the Operators on one side (Users with No Access, and Supervisors are not listed).
User Groups will also be listed, and users already assigned to groups are not listed. The list takes the form of a spreadsheet, with the names on the left, and the access rights on the right. By simply double-clicking on the displayed rights, access can be changed from Yes to No. Closing the screen is done by clicking on the Close button. So if the you wish to stop users Deleting Customers, then simply by going to the Customer Browse, and pressing Ctrl-F8, you can limit the access to the Delete button.