This blog talks about the Event Handling in c#.

An event is an action such as mouse click, a key press, mouse movement or any system-generated notification.  A process communicates through events.

Event is ASP.NET raised at the client machine and handled at the server machine.  For example, a user clicks a buttons displayed in the browser. A click event is raised. The browser handles this client-side event by posting it to the server.

The server has a subroutine describing what to do when the event is raised. It is called the event-handler. Therefore, when the  event message is transmitted to the  server. It checks whether the click event has an  associated event handler.

Event Arguments:

ASP.NET event handlers generally take two  parameters and return void. The first parameter represents the object raising the event and the second parameter is event argument.

Syntax of an event is:

Void Event name(Object sender, EventArgs e)
You want to learn event delegate What is Event delegate?