Some components have a default event, which is the event the component most commonly needs to handle. For example, a button's default event is OnClick. To create a default event handler, double-click the component in the Form Designer; this generates a skeleton event-handling procedure and opens the Code editor with the cursor in the body of the procedure, where you can easily add code. 

Not all components have a default event. Some components, such as TBevel, don't respond to any events. Other components respond differently when you double-click them in the Form Designer. For example, many components open a default property editor or other dialog when they are double-clicked at design time.