PDO + DAO, am I doing this right?

Question

I started to take a look at PDO and DAO but still do not understand how to do right.

I had some problems with the function bindParam that does not pass get method then I had to do a gambit.

And also how to handle the connection. I must pass the connection object in PDO?

What’s the right way to do it?

Follow the connection code, class, classeDAO and main (config_banco.php is where I save the connection data)

connect PDO.php:

include_once $_SERVER['DOCUMENT_ROOT']."/config.php"; 
include DIR_MODEL."config_banco.php";

function conectar (){
    $cfg = new ConfigBanco();       
    try{            
        $db = new PDO("{$cfg->nomeSGBD}:host={$cfg->enderecoHost};dbname={$cfg->nomeBanco}",
                        $cfg->usuarioBanco,$cfg->senhaBanco);
        return $db;

    }
    catch(PDOException $e){
        echo $e->getLine() ." ". $e->getMessage().$cfg->usuarioBanco;
        exit();
    }   

}

Php user.:

<?php
include_once $_SERVER['DOCUMENT_ROOT']."/config.php";
class Usuario{

   private $login;
   private $senha;
   private$nome;
   ...
   //Tenho aqui o construtor,os métodos get e set.  
}
?>

User.php:

<?php

 include_once $_SERVER['DOCUMENT_ROOT']."/config.php";
 include_once DIR_MODEL."conectarPDO.php";
 include_once DIR_MODEL."usuario.class.php";

 class UsuarioDAO extends Usuario implements interfaceDAO {

     public $pdo;   

     public function __construct($pdo){
        $this->pdo = $pdo;
     }
     public function getPdo(){
        return $this->pdo;
     }
     public function inserir($usuario) {

        global $pdo;                         
        $sql = "INSERT INTO `usuario`
                (`login`, `senha`, `nome`)
                VALUES (?,?,?)";


        $result = $pdo -> prepare($sql);
        //bindParam não aceita método get
        $login = $usuario->getLogin();
        $senha = $usuario->getSenha();
        $nome = $usuario->getNome();

        $result->bindParam(1, $login);
        $result->bindParam(2, $senha);
        $result->bindParam(3, $nome);

        $result->execute();     

     }
}
?>

And a main just to test:

<?php 
    $usuario = new Usuario("login","nome,"senha");
    $pdo =  conectar(); 
    $usuarioDAO = new UsuarioDAO($pdo);
    $usuarioDAO->inserir($usuario);
?>

Thanks for the help.