how add js files to create a responsive theme?
Copy the plugin on your subtheme's folder like "plugins/fullpage/".

Edit subtheme.info file adding:

stylesheets[all][] = plugins/fullpage/jquery.fullPage.css
scripts[] = plugins/fullpage/jquery.fullPage.min.js

Check if you need to add the other js files like vendor/jquery.easings.min.js, jquery.slimscroll.min.js...

It seems that the plugin needs jQuery 1.9.1 so https://drupal.org/project/jquery_update may be helpful

More info about the plugin: https://github.com/alvarotrigo/fullPage.js