How to record local3 with all severity levels to a file using system logger?

I'm using a VM. Ubuntu Linux. What I'm trying to do is use System logger to record the local3 facility with all severity levels to a file /var/log/local3.log I'm confused as to what the process is. Am I just supposed to edit /etc/rsyslog.conf with something along the lines of: local3.* /var/log/local3.log or do I use the logger command? Or both? I also want to add a logrotate afterwards so that it rotates weekly, keeping 8 weeks worth of log files.