Database Connection

I am using visual studio 2010. I had created a registration page and login in page. In the registration page, user had to key in username and password and it will be store in the database. How do I link the database from registration page to login page so that I can check whether the user had key in the correct password or whether the user had registered aldready.
I'm using c# and Microsoft SQL management studio.
Thank you in advance.


protected void Button1_Click(object sender, EventArgs e)
        {
 
  SqlConnection conDatabase = null;
  string username = TextBox1.Text;
            string password = TextBox2.Text;
            SqlConnection connection = null;
            SqlCommand command = null;
            SqlDataReader dataReader = null;
            try
            {
                string connectionString = ConfigurationManager.ConnectionStrings["TestConnectionString"].ConnectionString;
                connection = new SqlConnection(connectionString);
                connection.Open();
                //prepare sql statements
                string sql = "SELECT * from Staff where username='" + username + "'And Password='" + password + "'";
                command = new SqlCommand(sql, connection);
                dataReader = command.ExecuteReader();
                while (dataReader.Read())
                {
                    username = dataReader.GetString(3);
                    Session.Add("username", username);
                   
                }
                dataReader.Close();
            }
  catch catch (IndexOutOfRangeException)
  {
  username.Text = "";
  password.Text = "";
  {
  Response.Write(ex.Message);
            }


May I know if this is correct or do I need to add more things?