There is no one port number for a computer. Computers use multiple ports to accommodate different processes running on the computer. The port number in use varies on the software or service being used and the computer's configuration.
Ports that are universally agreed upon for use with specific services are in the System or Well Known Port range from 0 to 1023. These commonly used ports include ports 80 and 443 for HTTP and HTTPS, which are used by an Internet browser to access Web pages, along with port 23 for Telnet, used to log into a remote computer, and ports 20 and 21 for FTP, or File Transfer Protocol.