There is no sample file, but you can follow the steps in the Storyline tutorial because they are very similar: https://cluelabs.com/tutorials/09-google-sheets-course-data-export/export-storyline-to-google-sheets/index.html#/

Also, when you set up your sheets document, you will get a list of steps to implement it in Captivate.

You need to use the JavaScript interface for Adobe Captivate to get a variable value into a JS variable. Here's a description provided by Adobe: https://helpx.adobe.com/in/captivate/using/common-js-interface.html