The Firewall and IP Permissions
Like setting up wireless, setting up firewall permissions and IP permissions depends on the modem/router interface, and again requires the ISP's technical support.
A physical firewall, like the ones built into routers, help to protect all computers hooked up to the router from external assaults, such as hackers or viruses, by blocking incoming and outgoing information on ports for which it has no information. This means that if the user wants to use a program that needs a certain port, such as an FTP program or an online game, the system administrator first has to tell the firewall about the ports that need opening. The first step is to know which port to open. How exactly to open it depends on the specific modem/router, and is best left to the ISP's technical support.
Typically, when a computer hooks up directly to the Internet, it gets a public IP. Viruses and hackers attack the IP. By hooking up a router, the router gets the public IP, thereby absorbing all attacks, and thus protecting all the computers hooked up behind it. To allow all the computers behind the router to reach the Internet, the router will dish out its own internal IPs. All routers use the same basic range, 192.168.x.x (the x's can be any number between 0 and 256). The router uses these IPs to ensure that each computer on the home network gets the information requested and nothing else. Since file and printer sharing also depend on these IPs, the IP allotted to a specific computer does not change.
Use this basic understanding of what a modem and a router is, learn more about how to set up these devices, and find out what they can do to improve your home network so you can get started on a great networking career!