A "port" is an IT term for socket. The RJ11 port is found in millions of homes and businesses all over the world. It is the phone socket. Although, strictly speaking, "ports" are only found on computers, the same socket can be found on telephones, fax machines and in wall sockets.
Many computers have an RJ11 port. On laptops it is usually on the side of the computer, on desktop computers it will be at the back, or on the front somewhere near the DVD tray. The main purpose of this socket is to connect to dial up modems. The RJ11 jack is usually immediately next to another socket, which looks almost the same, only is a little wider. This is the RJ45 network socket and is the more usual connector nowadays to connect to a DSL Internet service. Both these sockets are wired to a network adaptor, which is responsible for converting computer data into a format acceptable to the network.
It is possible to connect the telephone line to the RJ11 port on a computer to receive calls. This configuration requites call management software that is compatible with the network adaptor. Such software usually provides the capability to receive faxes and store them as computer files. It usually also enable the user to create a switchboard structure with extensions and voice mail. Calls can be directed to an automated message, or placed on hold where the caller listens to music or a message recorded on the computer.
The regular location for an RJ11 port is on a telephone or fax machine. The wall plate by which the phone line enters a house also has an RJ11 socket. The plug in all instances is the same and the ports of each different piece of equipment also follow the same standards.
The RJ11 port contains six channels at the bottom, each with a copper metal strip. This strip is a contact and creates a connection when corresponding metal strips in the plug tough the socket strips. The plug is held in place with a plastic spring at the top. A phone line travels over two wires, and so only the two central contacts actually connect to anything. The remaining four contacts can be used to add in two more lines entering the computer or telephone.