how i use global.asax page for logout current session on close browser

Your web application starts as soon as the first visitor hits your page. For each different user, a session will be created. A session has a certain expiration. If the user stops browsing your website, the session expires after expirationTime of the last hit on your server. (expirationTime has a default of 20 minutes)

Each time a session expires, the method above will be executed.
After the last session expires, also Application_End() will be executed.

You cannot call the method manually to expire sessions when you want.

Eduard