Here is one I found on Google that has the most comments I have ever seen on a file:

http://oceanpark.com/notes/firewall_example.html

Be aware that the above was written to be run on Red Hat, look out for OS specific commands. Mostly should be fine.

If you are not familiar with scripts..

you can use "webmin" for your purpose

download it from "webmin.com"

In iptables u first drop all roules

then any port and ip to need open

iptable action ip port