This article is not made for technical person though if you are a network kiddy or if you are searching for a startup on NAT this article is a good place to start. I assume you might have knowledge of public ip and private ip if not click here.
Network Address Translation(NAT) or Port forwarding is mostly used in small to large companies but it can also be use in home or educational and playing purpose like setup you own home webserver or call server and so on.
nat is a feature which come with atmost all routers and broad band modems even which comes for home internet plan.
Nat is used to show a group of computer(Private ip address LAN) in one single IP address(mostly Public IP address). If you enable nat in your router and if you configure it properly then you can access your computer from your friends computer or office or outer place any where.
If you have your webserver IIS, Apache, XAMP etc(port 80) which runs on 192.168.1.10 private ip address and javaserver Tomcat, glassfish etc(port 8080) which runs on 192.168.1.15 private ip address both can be accessed from outer network on 184.108.40.206 (public ip address ISP will give it for every broad band internet connection). So you can have more than one server service which runs on one ip.