A push button is a rectangle containing application-defined text (label), an icon, or a bitmap that indicates what the button does when the user selects it. A push button can be one of two styles: standard or default, as defined by the constants BS_PUSHBUTTON and BS_DEFPUSHBUTTON. A standard push button is typically used to start an operation. It receives the keyboard focus when the user selects it. A default push button, on the other hand, is typically used to indicate the most common or default choice. It is a button that the user can select by simply pressing ENTER when a dialog box has the input focus.
When the user selects a push button (of either style), it receives the keyboard focus from Windows, which sends the button's parent window a WM_COMMAND message containing the BN_CLICKED notification code. In response, the dialog box typically closes and carries out the operation indicated by the button.