Perloo is a free app that has no 'help' page, no screen of instructions. It starts in black, and then a man in a meadow ruminates philosophically. The screen goes black again and you see a round white-and-black shape. It soon becomes obvious that the white shape responds to movement of your iPhone.
From there, I have no advice to give you. As you go deeper, the game gets more intensive and frustrating. Keep at it. There are worlds to discover and explore. I'm not sure how far I am into the game, and how far there is to go. That's one of the joys of how it all works.
Even the game icon (see above) is puzzling. It looks like just black at first glance, but a closer look barely reveals a shape.
I have seen some games, the 'Myst like' games that create a physical place you can explore. But Perloo is completely abstract, and yet physical rules apply. The sounds are excellent, and it is hard not to get involved.
Perloo is not universal, so it's best played on an iPhone or an iPod touch. It requires iOS 6 or better. Although I didn't try, I'll bet headphones further enhance the game experience.
Beware the prism level. Enough said.