If you've ever done any Web page design or programming, you're undoubtedly familiar with the structure of a link in HTML. In technical terms, an HTML link uses the anchor element (whose starting and ending tags are <a> and </a>), and one of its main attributes, href, which has a URL as its value. Text or images placed inside the beginning and ending <a> tags make a link that, when clicked, goes to the URL in the href attribute, like this:

<a href="">Click Here</a>

So clicking a link is one form of user interaction enabling you to communicate with the server. But it's pretty limited, because all you can do is make a request for the page that's already supplied by the site designer. For example, if I click a link to the About page, the only reason it goes to the right page is because the site designer has already hard-coded the link with the URL for that page.