<?php // file: animal.php
 
Class Animal
{
      $name;
      $noise;
 
      function _construct($nm, $no)
      {
            $this->name = $nm;
            $this->noise = $no;
      }
 
      function noise()
      {
            return $this->$noise;
      }
}
 
$dog = new Animal("dog", "Woof!");
 
?>

include_once("dir/clsAnimal.php");
 
$dog = new Animal("dog", "Woof!");
$noise = $dog->noise();
echo $noise;
 
NOTE: Within your class your instance variables '$noise' and '$name' you should declare them specifying the type of variable it is.
 
Being 'public' 'protected' or 'private'.
eg:
public $noise; 
public $name;

<?php    //animal.inc
 
class Animal
{
    private $noise;
 
    function __construct($param)
    {
        $this->noise = $param;
    }
 
    function makeNoise()
    {
        return $this->noise;
    }
}
 
?>

<?php    //instantiate.php
 
    require('animal.inc');
 
    session_start();
 
    $dog = new Animal("Woof!");
 
    $_SESSION[obj] = $dog;
 
?>

<?php    //call.php
 
    require('animal.inc');
 
    session_start();
 
    echo " a dog goes woof";
 
    $dog = $_SESSION[obj];
 
    //error on next line
    //$noise = $dog->makeNoise();
?>