Firewalld can be managed using firewall-config (GUI) and firewall-cmd (CLI), but YaST also provides a basic configuration tool for firewalld as well.
The really confusing thing is that the YaST module is loaded by default it seems at least on Tumbleweed and I think Leap 5.2 and people seem to use it because it’s there.
Yes, it can be used for simple firewall configuration, but firewalld’s native tools are obviously more comprehensive.