In LoginPage.aspx's Login button storing Session["username"].

protected void btnLogin_Click(object sender, EventArgs e)
    {
if (CheckUserCredentials(txtUserName.Text.ToString().Trim(), Encrypt(txtPassword.Text.ToString().Trim(), true)))
{

if (dtLoginuserDetails.Rows.Count > 0)
{
                          Session["username"] = txtUsername.text;
}
}

Sample.aspx

Using Session["username"] in sample.aspx, if it is k then it will open sample.aspx

protected void Page_Load(object sender, EventArgs e)
    {
        if ((Session["username"] == null) || (Session["username"] == "") || (Session["username"] == string.Empty))
        {
            Server.Transfer("sample.aspx");
            return;
        }
In Logout.aspx use the below..
Session.Abandon();
will close the session

//Initialize - During login in inside of login button click event
session["loginuser"] = "name of the user";

//Calling like this
 Label1.Text = Session["loginuser"].ToString();

//Remove like this
Session.Remove("loginuser");

//Remove all session values
Session.RemoveAll();