A set of Web pages that go together, generally belonging to one company, person or organization. Every computer that's connected to the Internet has a unique, numeric address. Don't worry you don't have to know any of them. People generally prefer to remember words and names rather than numbers, so a system has been developed to assign names to these numbers. These are called domain names.
Domain names have levels top level, second level, and so on.
A piece of data in a computer. A byte can hold one letter or other character, or a numerical value, or an instruction for the computer. It's really not that bad. The system of clicking on a link on a Web page and thus going to a different page is called Hypertext.