A web browser is an application software used to access the web. Web browsers understand HTML, CSS, and Javascript and render the web pages to the visitors. Web browsers, such as Netscape, Opera, and IE contact remote web servers and make requests on behalf of users. The documents can contain hyperlink points (links) to other documents, which may or may not live on the server that the user originally contacted. Once the browser receives response to its request, it processes the code as depicted in the following diagram:

When browsers send requests to servers for HTML files, those HTML files often contain <link> elements referencing external CSS stylesheets and <script> elements referencing external JavaScript scripts. It's important to know the order in which those files are parsed by the browser as the browser loads the page:

1. The browser parses the HTML file first, and that leads to the browser recognizing any <link>-element references to external CSS stylesheets and any <script>-element references to scripts.
2. As the browser parses the HTML, it sends requests back to the server for any CSS files it has found from <link> elements, and any JavaScript files it has found from <script> elements, and from those, then parses the CSS and JavaScript.
3. The browser generates an in-memory DOM tree from the parsed HTML, generates an in-memory CSSOM structure from the parsed CSS, and compiles and executes the parsed JavaScript.
4. As the browser builds the DOM tree and applies the styles from the CSSOM tree and executes the JavaScript, a visual representation of the page is painted to the screen, and the user sees the page content and can begin to interact with it.