Tell composer to require HoussradMangoPayBundle by running the command:
$ php composer.phar require "houssrad/mangopaybundle:dev-master"
Composer will install the bundle to your project's vendor/houssrad/mangopay-bundle
directory.
Finally, enable the bundle in the kernel:
<?php
// app/AppKernel.php
public function registerBundles()
{
$bundles = array(
// ...
new Houssrad\MangoPayBundle\HoussradMangoPayBundle(),
);
}