You've now built a dialog with three push buttons and a list box. At this stage in the design, you'll often refine the order of controls, that is, the order in which the user will move through them with the TAB key.
When the user of your dialog box presses the TAB key, the focus moves through the controls in order, stopping at each one for which a tab stop is set. Some controls, such as a frame, have no need for a focus. Controls that can use the focus have a tab stop set by default. Each control in your dialog already has a tab stop.