The bundle just integrates the Ivory Serializer library into Symfony. In order to use the library, you can fetch the serializer from the container and use it for serializing or deserializing your data:
use Ivory\Serializer\Format;
$stdClass = new \stdClass();
$stdClass->foo = true;
$stdClass->bar = ['foo', [123, 432.1]];
$serializer = $container->get('ivory.serializer');
echo $serializer->serialize($stdClass, Format::JSON);
// {"foo": true,"bar": ["foo", [123, 432.1]]}
$deserialize = $serializer->deserialize($json, \stdClass::class, Format::JSON);
// $deserialize == $stdClass