WWW is an acronym for World Wide Web, the first thing to emphasize is that it is not a synonym for the internet. The World Wide web or just the Web is a subset of the internet, a system of Internet servers that support formatted documents, web pages. These documents are formatted in a markup language called HTML (Hypertext Markup Language) that not only supports links to other pages, but also graphics, audio and video files (think of youtube ;). Not all Internet servers are part of the World Wide Web.
The world wide web is a way of accessing information over the internet, it consists of pages that can be accessed using a Web Server.
The Internet is the actual network of networks where “everything” is stored and can be accessed. Things like emails, SMTP, FTP, Telnet, chat (IRC) and Internet Gaming and much more are all part of the internet but not part of the web.
The web pages are transferred from the web to our computers with the help of the Hyper-Text Transfer Protocol (HTTP), which is a protocol / set of rules which allows the access to HTML pages which work together with HTTP.
The simplest way to understand the world wide web / the web is to imagine a browser and the way you look for and access web pages, you are using the web right now.