• Camada de Apresentação - UI - Presentantion Layer
• Camda de Negócios - BLL - Business Logic Layer
• Camada de Acesso aos Dados - DAL - Data Access Layer
• Fonte de dados - Data Source

Public Class Cliente

    Public Property Id As Integer
    Public Property Nome As String
    Public Property Endereco As String
    Public Property Telefone As String
    Public Property Email As String

End Class

Imports System.Data
Imports System.Data.SqlClient
Imports System.Collections.ObjectModel
Imports CamadaDeTransferencia

Public Class ClienteDAL

    Private connStr As String = Nothing

    Sub New()
        connStr = "Data Source=.\sqlexpress;Initial Catalog=Cadastro;Integrated Security=True"
    End Sub

    Public Function CarregaDadosDataReader() As List(Of Cliente)

        Dim lista = New List(Of Cliente)()
        Using conn As New SqlConnection(connStr)
            Using cmd As New SqlCommand("Select * from Clientes", conn)
                cmd.CommandType = CommandType.Text
                conn.Open()
                Using reader As SqlDataReader = cmd.ExecuteReader()
                    While reader.Read()
                        Dim p As New Cliente() With { _
                             .Id = reader.GetInt32(reader.GetOrdinal("id")), _
                             .Nome = reader.GetString(reader.GetOrdinal("nome")), _
                             .Endereco = reader.GetString(reader.GetOrdinal("endereco")), _
                             .Telefone = reader.GetString(reader.GetOrdinal("telefone")), _
                             .Email = reader.GetString(reader.GetOrdinal("email")) _
                        }
                        lista.Add(p)
                    End While
                End Using
                conn.Close()
            End Using
            Return lista
        End Using
    End Function

    Public Function CarregaDadosDataTable() As Collection(Of Cliente)
        Dim colecao = New Collection(Of Cliente)()
        Using conn As New SqlConnection(connStr)
            Using cmd As New SqlCommand("Select * from Clientes", conn)
                cmd.CommandType = CommandType.Text
                Using ad As New SqlDataAdapter(cmd)
                    Dim table As New DataTable()
                    'abre a conexao
                    conn.Open()
                    ad.Fill(table)
                    conn.Close()
                    ' percorre todas as linhas
                    For Each row As DataRow In table.Rows
                        Dim p As New Cliente() With { _
                             .Id = Integer.Parse(row("id").ToString()), _
                             .Nome = row("nome").ToString(), _
                             .Endereco = row("endereco").ToString(), _
                             .Telefone = row("telefone").ToString(), _
                             .Email = row("email").ToString() _
                        }
                        colecao.Add(p)
                    Next
                End Using
            End Using
            Return colecao
        End Using
    End Function
End Class

using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Collections.ObjectModel;
using CamadaTransferencia;

public class ClienteDAL
{

    private string connStr = null;
    public ClienteDAL()
    {
        connStr = "Data Source=.\\sqlexpress;Initial Catalog=Cadastro;Integrated Security=True";
    }

    public List<Cliente> CarregaDadosDataReader()
    {
        var lista = new List<Cliente>();
        using (SqlConnection conn = new SqlConnection(connStr))
        {
            using (SqlCommand cmd = new SqlCommand("Select * from Clientes", conn))
            {
                cmd.CommandType = CommandType.Text;
                conn.Open();
                using (SqlDataReader reader = cmd.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        Cliente p = new Cliente
                        {
                            Id = reader.GetInt32(reader.GetOrdinal("id")),
                            Nome = reader.GetString(reader.GetOrdinal("nome")),
                            Endereco = reader.GetString(reader.GetOrdinal("endereco")),
                            Telefone = reader.GetString(reader.GetOrdinal("telefone")),
                            Email = reader.GetString(reader.GetOrdinal("email"))
                        };
                        lista.Add(p);
                    }
                }
                conn.Close();
            }
            return lista;
        }
    }

    public Collection<Cliente> CarregaDadosDataTable()
    {
        var colecao = new Collection<Cliente>();
        using (SqlConnection conn = new SqlConnection(connStr))
        {
            using (SqlCommand cmd = new SqlCommand("Select * from Clientes", conn))
            {
                cmd.CommandType = CommandType.Text;
                using (SqlDataAdapter ad = new SqlDataAdapter(cmd))
                {
                    DataTable table = new DataTable();
                    //abre a conexao
                    conn.Open();
                    ad.Fill(table);
                 //fecha a conexão
                    conn.Close();
                    // percorre todas as linhas
                    foreach (DataRow row in table.Rows)
                    {
                        Cliente p = new Cliente
                        {
                            Id = int.Parse(row["id"].ToString()),
                            Nome = row["nome"].ToString(),
                            Endereco = row["endereco"].ToString(),
                            Telefone = row["telefone"].ToString(),
                            Email = row["email"].ToString()
                        };
                        colecao.Add(p);
                    }
                }
            }
            return colecao;
        }
    }
}

Imports CamadaDeNegocios
Imports CamadaDeTransferencia

Public Class Form1

    Private Sub btnSair_Click(sender As Object, e As EventArgs) Handles btnSair.Click
        Me.Close()
    End Sub

    Private Sub btnCarregaDadosDataReader_Click(sender As Object, e As EventArgs) Handles btnCarregaDadosDataReader.Click
        dgvClientes.DataSource = New ClienteBLL().CarregaDadosdoDataReader
    End Sub

    Private Sub btnCarregaDadosDataTable_Click(sender As Object, e As EventArgs) Handles btnCarregaDadosDataTable.Click
        dgvClientes.DataSource = New ClienteBLL().CarregaDadosdoDataTable
    End Sub
End Class

using System;
using System.Windows.Forms;
using CamadaDeNegocios;


namespace CamadaApresentacao
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void btnDataReader_Click(object sender, EventArgs e)
        {
            dgvClientes.DataSource =  new ClienteBLL().CarregaDadosdoDataReader();
        }

        private void btnDataTable_Click(object sender, EventArgs e)
        {
            dgvClientes.DataSource = new ClienteBLL().CarregaDadosdoDataTable();
        }
    }
}