Q: What does the price include?
Answer: The $35 price is for each separate can rotator device. Some of the pictures show multiple devices mounted next to each other.
Q: How are the devices secured to a wall?
Answer: As they can be quite heavy when fully loaded, they need to be securely screwed into a wood backing - either a solid sheet such as plywood or several horizontally mounted boards which are screwed into studs.
Q: How much clearance is required underneath the devices to allow the removal of the cans?
Answer: 1.5" to 2" is recommended underneath them if multiple devices are mounted next to each other.