Suppose you have to enter into your account. Now, a session variable created after login and you want to pass this value in page title. If you have a master page then simple use this code in code behind page. Also you can use this code in web form. Lets take a simple example

Use only Business Logic code

public partial class Default5 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        Session["username"] = "- ASP.NET CODE";
        Page.Title += Session["username"].ToString();
    }
} 

Code Generate the following Output