use Monolog\Logger;
use Monolog\Log;
use Monolog\Writer\FileWriter;
use Monolog\Formatter\SimpleFormatter;
// create a log with writers/formatters
$writer = new FileWriter('path/to/your.log');
$writer->setFormatter(new SimpleFormatter());
$log = new Log('name', Logger::WARN, $writer);
// create a logger with one or more logs
$logger = new Logger(array($log));
// write to all logs
$logger->warn('Foo');
// write only to the 'name' log
$logger->error('Bar', 'name');