You know what a website is, but you’re not sure what a website is.
The best way to think about a website is simply as a group of files. Files just like the ones on your hard drive, organized into folders. Except instead of files that end in .doc and .mp3, these files end in things like .html and .jpg. Website files are kept on a server and delivered to your browser when you ask for them by visiting a particular URL. Your browser analyses them and renders them to the screen.
So next up we are going to make a very small website which will live on your hard drive. People won’t be able to access this website while it is on your hard drive, but it will allow you to build it. When it is ready you can put it on a server on the Internet and then bang. Live website.