use Aws\S3\S3Client;
use League\Flysystem\AwsS3v2\AwsS3Adapter;
use League\Flysystem\Filesystem;

$client = S3Client::factory(array(
    'key'    => '[your key]',
    'secret' => '[your secret]',
    'region' => '[aws-region]',
));

$adapter = new AwsS3Adapter($client, 'bucket-name', 'optional-prefix');

$filesystem = new Filesystem($adapter);