The Internet port number depends on how a computer is connecting to the Internet; for example, if the computer is connecting to http websites, it uses port 80. Ports 0-1023 are reserved for specific services used by the Internet host. Other examples include, port 21 for FTP, port 23 for telnet and port 53 for DNS.
A port acts like an electronic docking point to connect computers to each other through a network or to connect computers to the Internet to keep information flowing. Ports 1024 to 49151 are registered to specific companies for use by their protocols. Ports 49152 to 65536 can be used by anyone with an Internet connection.