Drupal includes the Database Logging module, which logs and records system events to the database. When database logging is enabled, you can go to
/admin/reports/dblog on your site and see recent log entries.
If, on the other hand, the Syslog module is enabled, you will find the log messages in your standard operating system logs. See https://www.drupal.org/documentation/modules/syslog for details.
The following pages provide information about error messages that you might encounter in your Drupal logs.