ช่วยอธิบาย Concept Code C# พวกนี้ให้หน่อยสิครับเป็น Code ประเภท OleDb อ่ะครับ

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.OleDb;
using System.IO;

namespace LoginFormCS
{
    public partial class frmLogin : Form
    {
        public frmLogin()
        {
            InitializeComponent();
        }

        private void btnLogin_Click(object sender, EventArgs e)
        {
            OleDbConnection objConn = new OleDbConnection();
            OleDbCommand objCmd = new OleDbCommand();
            string strConnString = null;
            string strSQL = null;
            string directory = Path.GetDirectoryName(Application.ExecutablePath);

            strConnString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + directory + "\\database.mdb;Jet OLEDB:Database Password=;";
            objConn.ConnectionString = strConnString;
            objConn.Open();

            int intNumRows = 0;
            strSQL = "SELECT COUNT(*) FROM member WHERE Username = '" + this.txtUsername.Text + "' AND [Password] = '" + this.txtPassword.Text + "' ";
            objCmd = new OleDbCommand(strSQL, objConn);
            intNumRows = Convert.ToInt32(objCmd.ExecuteScalar());

            if (intNumRows > 0)
            {
                frmMain frm = new frmMain();
                frm._strUser = this.txtUsername.Text;
                frm.LoadInfor();
                frm.Show();

                this.Hide();
            }
            else
            {
                MessageBox.Show("Username or Password Incorrect");
            }

            objConn.Close();
            objConn = null;
        }

        private void btnClose_Click(object sender, EventArgs e)
        {
            if (MessageBox.Show("Exit application?", "", MessageBoxButtons.YesNo) == DialogResult.Yes)
            {
                Application.Exit();
            }
        }


    }
}