How to set up a firewall using FirewallD on OpenSUSE Linux

Originally published at: https://www.cyberciti.biz/faq/set-up-a-firewall-using-firewalld-on-opensuse-linux/

I am a new OpenSUSE Linux 15.x sysadmin. How do I set up a firewall using FirwallD on OpenSUSE Linux 15.1?