Answers for "how to start and destroy the session?"

php delete session

session_destroy(); // To delete whole session
// OR
unset($_SESSION['myVar']); // To delete a session var

Remove Session

Response.Cache.SetExpires(DateTime.UtcNow.AddMinutes(-1));
Response.Cache.SetCacheability(HttpCacheability.NoCache);
Response.Cache.SetNoStore();
Session.Abandon();
Session.Clear();