How to use request.QueryString

It is used to get values which is in querystring in browser url.

For eg. For url: www.asc.com?value=test

value "test" in url can be find like

string qValue = Request.QueryString["value"];

QueryString is used to pass data from one page to another or one website to another

http://www.dotnetperls.com/querystring

In addition, have you tried searching the web about it? I'm sure it will give you lot's of information about it. Here's one from msdn: http://msdn.microsoft.com/en-us/library/ms524784%28v=vs.90%29.aspx