How to use rubber backscratcher/massager.?

For my birthday, my friend got me this rubbery backscratcher/massager about 8 inches long with 2 flashing bulbs on the opposite end and like a knob on top and when i turn it on. It just vibrates and the knob turns around a bit so it doesn't really scratch my back well. Apparently its for use all over the body. Is there a tequnique to using those backscratchers cos apparently it was pretty expensive and it doesn't really help much.