$client = new JsonApiClient(
    'http://example.com/api',
    $httpClient, // instance of Psr\Http\Client\ClientInterface
    $uriFactory, // instance of Psr\Http\Message\UriFactoryInterface
    $requestFactory, // instance of Psr\Http\Message\RequestFactoryInterface
    $streamFactory, // instance of Psr\Http\Message\StreamFactoryInterface
    new Serializer(),
    new Deserializer()
);

$request = $client->createGetRequest(new Uri('/myResources/1')); // will fetch the resource at http://example.com/api/myResources/1
$request->requestInclude('myRelationship'); // include a relationship

$response = $client->execute($request);

$document = $response->document();
$myResource = $document->data()->first(); // the resource fetched by this request
$myIncludedResources = $document->included()->all(); // the included resources fetched with the include parameter