The best example of a WAN is the Internet.
WANs are used to connect local area networks together, so that users and computers in one location can communicate with users and computers in other locations.
Many WANs are built for one particular organisation and are private, others, built by Internet service providers provide connections from an organisation's LAN to the Internet.
WANs are most often built of leased lines. At each end of the leased line, a router connects to the LAN on one side and a hub within the WAN on the other.
Now that the Internet provides a high speed WAN, the need for a private network made up of leased lines owned by the organisation who wants to connect the sites has reduced, and a virtual private network is often used, which uses encryption and other techniques to make it appear that the organisation has a dedicated network while making use of the shared infrastructure of the WAN.