Ports and Addresses

Intro
Ports are merely reference numbers used to define a service. Addresses are used to locate computers. It works almost like a house address.

Usages:
There is a numbering system to help the mailman locate the proper house to deliver customer's mail to. Without an IP numbering system, it would not be possible to determine where network data packets should go.

Examples:
Port 23 is used for telnet services, and HTTP uses port 80 for providing web browsing service. There is a group called the IANA (Internet Assigned Numbers Authority) that controls the assigning of ports for specific services.