Книга: Iptables Tutorial 1.2.2
This chapter has explained some of the layout of the different scripts, but specifically the rc.firewall.txt script. The layout and inner workings of scripts described here and those found in other places can differ tremenduously. Everyone has their own coding style and how we write rulesets or code or scripts differ from person to person, and the style you've seen here is my style.
The next chapter will give some brief introductions to the different scripts available within this document. They will give you some basic idea what scenarios the scripts where written for, and then you should hopefully have taught yourself enough to grasp the rest of the scripts on your own. All of these scripts are also available for download on the main site of this document.