Click on Snapping button in Edit Functions Toolbar to switch the snapping on. The snapping works with unsymbolized, graphic and image objects and with objects from symbols with status normal or protect. The snapping does not work with layout objects, objects from hiddens symbols and with background maps.
Enter the snapping tolerenace in screen pixel in OCAD Preferences in the menu Options and change Snapping Tolerance in the category Drawing and Editing. The default value is 5 pixels.