Modify the HTML/CSS/JS code from your favorite text editor and it'll automatically refresh your web browser to see the changes.
* Display the page you want to modify.
* Click the play button to run the extention to verify when you change any of the files (css, js or html) that are loaded into the page.
* When finished press the stop button.
Unfortunately for security reasons the extension of Google Chrome will not run in the File:// protocol,ie the application must run on a test server (eg Django development Web server, ISS Express, Apache, etc).
If your intention is to design a simple html page, I can recommend launch a console, cd to the target directory containing all your content and run "python -m SimpleHTTPServer 8080" (without quotes) it's a useful workaround on Linux or Mac, (or possibly with Python installed on windows)