The Geek Stuff posted a tutorial about adding Firewall rules to IPTables

This article explains how to add iptables firewall rules using the “iptables -A” (append) command.

“-A” is for append. If it makes it easier for you to remember “-A” as add-rule (instead of append-rule), it is OK. But, keep in mind that “-A” adds

  Linux IPTables: How to Add Firewall Rules (With Allow SSH Example)