How To check Session authentication in asp.net

 I hope that it will be beneficial for everyone.....

protected void Button1_Click(object sender, EventArgs e)
    {
        if (txtmajorhead.Text == "")
        {
            lbl_msg.Text = "User Name is required !";
        }
        else if (txtdescp.Text == "")
        {
            lbl_msg.Text = "Password is required !";
        }
        else
        {
            Parameter UserId = new Parameter(txtmajorhead.Text);
            Parameter Password = new Parameter(txtdescp.Text);
            SqlDataAdapter da = new SqlDataAdapter("select * from Login where UserID='" + UserId + "' and Password='" + Password + "'", con);
            DataSet ds = new DataSet();
            da.Fill(ds);
           
            if (ds.Tables[0].Rows.Count > 0)
            {
                Session["UserID"] = ds.Tables[0].Rows[0]["UserID"].ToString();
                for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
                {
                    if ((ds.Tables[0].Rows[i]["UserID"].ToString() == txtmajorhead.Text) && (ds.Tables[0].Rows[i]["Password"].ToString() == txtdescp.Text))
                    {
                        f = 1;

                        Response.Redirect("AddCategory.aspx");
                        break;
                    }
                }
            }
            if (f == 0)
            {

                lbl_msg.Text = "UserName And Password Are Incorrect";


            }
            txtmajorhead.Focus();

        }