Want to understand how firewalld works

[marel]

If you are starting better switch to nft.

See:

Need help understanding firewall configuration in Leap

The nftables packet filter implimentation is a successor to iptables (as part of the Netfilter Project). The latter is kept for compatibility/legacy reasons, but by default Firewalld is now using the nftables backend. Firewalld has a graphical front-end provided by the firewall-config package. YaST provides a simpler graphical front-end, albeit with less functionality, (and which I personally don’t tend to use at all). Some reading: