can any one reply the answer?

Event can be associated with any objects like it could be textbox, buttons
etc that you use to create the user interface.
Now it's an action that is generated on performing any validations by pressing such as button and there is an event handler that handles the action and does the required task.That is why you see something like this
private Button1.click(e source)handles button1.click.
It is not as exact as it comes but yes it can make you understand what is an event handling.

Thanks