To use this feature please make sure you have installed all required plugins. This post Require Advanced Custom Fields, and One Click Demo Import plugins that available after you installing add on.
If those plugins never installed to your site, you will get a notification bar at the top of your admin dashboard.
Just click "Begin installing plugin" and activate it after installed.
Now, to make your site content same as our demo site. You need to import the content.xml from our demo site. After installing plugins, go to Appearance > Import Demo Data.
You will directed into Import demo page.
Hit the Import Demo Data button and wait for a minutes until your demo successfully installed.