Add the BarcodeScanner element to the page and this will also act as the video preview for the Barcode Scanner. The options can then be set on this element.
You start / stop the barcode scanning via workflow element actions.

Once the element gets visible on the page it will retrieve the current cameras on the device and store them in the 'Cameras' list state. These can be used to select the required camera. This has been added as an example in the demo page @ https://barcode-scanner-plugin.bubbleapps.io

Once the Barcode Scanner has scanned a barcode it will save the text to the 'Barcode Content' state and also save the image frame to the 'Image' state. If the file is saved to the db the URL of the image will be stored in the 'Saved Image URL' state too.