You only need to open these files if you are taking the Offline Course webpage course. If you double click the "index.html" file and it does not open in your browser, right-click the file and choose "Open With" then click "Choose another program." Then, select the browser that you would like to use for this course and check the box for "Always use this program to open .html files." The file should now open in your browser. (We recommend using Google Chrome or Firefox for your browser.)