How does music and video file sharing work?

There are many legal ways to buy music and movies over the Web.  Unfortunately, many people illegally obtain and share music, movie and other files with file sharing programs.  It works by downloading special software that connects your computer to other computers running the same software.  The software lets you find music or other files on other people’s PCs and download it.  This is called a peer-to-peer (P2P) network, because every PC is both a client and a server.