They're certainly nice to have, I think. [But hey, some people do just fine without.]

It's basically a big electronic network that connects all the computers and cell phones in the world - well, the ones that hook up to it, anyway - so that anyone, anywhere can share information or access databases and do things like leave messages for each other, videos, write books, comics - you can share pretty much anything! Social networks usually use it and are just a small section of what you can share.