Metode 1
<?php
class profile() {
    var $username;
    var $andenVariabel;

    function setData($a,$b) {
        $username = $a;
        $andenVariabel = $b;
    }
}

$profil = new profile();
$profil->setData("brugernavn","blabla");

echo $profil->username;
echo $profil->andenVariabel;
?>

Metode 2 (min favorit)
<?php
class profile() {
    var $username;
    var $andenVariabel;

    function fetchUser($username) {
        // NOGET DB STUFF DER HENTER BRUGEREN
        $user = mysql.........;
        $username = $user["username"];
        $andenVariabel = $user["name"];
    }

    function displayProfile() {
        echo $this->username;
        echo $this->andenVariabel;
    }
}

$profil = new profile();
$profil->fetchUser("brugernavn");
$profil->displayProfile();
?>