INDEX
<?php
require_once("user.php");

$server = "localhost";
$user = "root";
$pass = "";
$database = "test";

$mysqli = new mysqli($server,$user,$pass,$database);


if (mysqli_connect_errno()){
    echo "falha ao conectar-se ao mysql:(".$mysqli->connect_errno.") ".$mysqli-connect_error;
    exit;
}
$User = new user($mysqli);


$User->setName("Pepe")
        ->setEmail("pepinho@gmail.com");



echo $User->insert();




user.php
<?php

class user
{
    private $db;
    private $name;
    private $id;
    private $email;


    function __construct(Mysqli $mysqli)
  {
        $this->db = $mysqli;
  }
      public function lista()
    {

      }
      public function insert()
    {
     $stmt = $this->db->stmt_init();
     $stmt->prepare("INSERT INTO user(name,email)VALUES(?,?)");
     $stmt->bind_param("s", $this->name);
     $stmt->execute();
     return $stmt->insert_id;

    }


      public function update()
     {

      }
      public function delete()
     {

      }



     //seters e geters
        public function getId()
    {
        return $this->id;
    }

    public function setId($id)
    {
        $this->id = $id;
        return $this;
    }

    public function getName()
    {
        return $this->name;
    }

    public function setName($name)
    {
        $this->name = $name;
        return $this;
    }

    public function getEmail()
    {
        return $this->email;
    }

    public function setEmail($email)
    {
        $this->email = $email;
        return $this;
    }
}