Guidedog is an utility for configuring some of the more advanced networking features of the Linux kernel, namely packet routing, IP Masquerade/Network Address Translation (NAT), and port forwarding.
This manual assumes a basic understanding of terms and concepts such as network protocols and IP addresses. The Guarddog documentation has a very quick explaination of IP address here. The How Stuff Works website also has good explaination of how the Internet works here.
Guidedog is intended to be used in combination with a separate firewall program such as Guarddog. Guidedog has the potential to expose your machine and networks to the broader Internet. This is why also using firewall is strongly recommended. Use Guidedog to make set up your packet routing, and at the same time use your firewall to ensure that only the right people can access any newly exposed machine and networks.