Why we use view state and session state in asp.net2.0?Explain?

View state and session state is used to retain the values of controls(Textbox,radiobutton,etc) in case of postback .....

Session state example :

1:Store values in session variable :

session["String"]="value";

2:Retrieve session variable value :

string getName=session["String"]

View state:

Just make EnableViewState property of the control to true....