Add the webblock to a screen, this should work instantly without any other setup.

The moment you open this on pc or phone your webcam permissions will be triggered and if you then show the marker it should show 3D objects.

It is possible that you'll need to zoom out to see them since the orientation isn't always perfectly in front of you.

You can go into the widget tree to change the a-marker tag for another marker preset.

You can change the premitives inside the a-marker to show other models.