The spreadsheet must be published to the Web so Google can generate the CSV data files for you.
- Select File > Share > Publish to the Web ...
- Select the sheet you would like to publish
Choose Comma-separated values (.csv) as the publishing format
If your spreadsheet has never been published before, press the Publish button
Copy the resulting .csv URL
In the Conference App Builder, add a new data source, label it so you know it's referring to your Google Sheet and select CSV URL as the Source. In the next step, paste the URL you copied from your Google Sheet web publishing step.