Global.asax is a file located in the root directory of your application. It is inaccessible over the web but is used by the ASP.NET application if it is there. It is a collection of event handlers that you can use to change and set settings in your site. The events can come from one of two places - The HTTPApplication object and any HTTPModule object that is specified in web.confg or machine.config. We will be covering both here.
How to create Global.asax?
Adding a Global.asax to your web project is quiet simple.
Open Visual Studio 2005 or 2008 -> Create a new website -> Go to the Solution Explorer -> Add New Item -> Global Application Class -> Add.