Log files contain important information about what happened in your environments. They should be your first step when troubleshooting, because often an application code or configuration error is logged very clearly, allowing you to resolve the issue in no time.
Each node is configured with default logs as part of the server's standard configuration. You may wish to make changes to the log format, or if you're hosting multiple domains within one environment you may find it convenient to split the logs by domain. Consult the official server documentation for the configuration options.