View state is a property of a page and controls to store the values across the round trips. This value will be stored in the form of hashed string in one or more hidden fields that depends on the MaxStateFieldLength property. When the page is posted back to the server, the page parses the view-state string at page initialization and restores property information in the page.
Viewstate["SlightbookViewState"] = "Slightbook";
To access the value from a view state in the form of string.
string sb = Viewstate["SlightbookViewState"].ToString();