use Monolog\Logger;
use Monolog\Handler\StreamHandler;
use Superbalist\Monolog\Formatter;

// create a handler
$handler = new StreamHandler('path/to/your.log', Logger::WARNING);

// use custom formatter in handler
$handler->setFormatter(new GoogleCloudJsonFormatter());

// create a log channel
$log = new Logger('name');
$log->pushHandler($handler);

// add records to the log
$log->addWarning('Foo');
$log->addError('Bar');