The World Wide Web is NOT the Internet. The WWW is accessible over the Internet. It is a web of connected documents or resources. The links are placed within the pages so that a user can go from one to another easily.

Each Web page is held on a server.  You can make HTML pages without a server but to be Web pages they need to be on a server and accessible over the Internet. Typically a Web server will hold a whole load of pages organised as a Web site.

The World Wide Web may be referred to as The WWW, just the Web or even W3.

All a Web designer needs to know is that it exists and that it is made up of linked resources many of which are HTML pages which people will pay you to create for them.