To "activate" your auto. wipers, lift the wiper lever at the intermittent position (on a conventional car). Your sensor are located at center top of the windshield.
Put water your sensor to test it.
I don't like it. I use Aquapel, so i don't need wipers at all!
I think it is an extremely useful feature. I hate continually having to adjust wiper speed as the intensity of the rain changes. There is an adjuster that is like what you would normally use to set intermittent speed. It adjusts the sensitivity of the rain detector. I find that once I set the sensitivity the way I wanted it, the rain sensor works very well. The wipers do a good job automatically adjusting to the intensity of the rain as it changes.