Hi,
nhibenate is used to map object data model and relation data model.
you can find lot of articale about that in goole....
here is the tutorials for this
http://www.codeproject.com/KB/database/Nhibernate_Made_Simple.aspx
http://www.codegod.de/WebAppCodeGod/nhibernate-tutorial-1---and-aspnet-AID25.aspx
NHibernate is an Object Relational Mapper (ORM) tool - which is to say it takes your living, squirming objects from a running application and stuffs them into some kind of database. It also will be happy dig into the database, grab some sleeping object, shake it awake and toss it back into your running application when you need it.
There are many links which take you to the learning of NHibernate just a search away for you :)
http://www.hanselman.com/blog/LearnHowToUseNHibernateWithTheSummerOfNHibernateScreencastSeries.aspx
http://www.thefreakparade.com/2008/07/so-you-want-to-learn-nhibernate-part-12-prerequisites-or-nhibernate-marijuananet/