Actually I had to unscrew the rotary part of my dishwasher in order to clean it. There was gunk blocking the flow of the jets. Anyway, that's how you do it, you can unscrew that part.

Another thing you need to know is that the little mysterious plug on the sink is how the dishwashing-water gets down the drain. It can get plugged. Twist off the chrome cap then unscrew the plastic.

A needlenose pliers and kabab skewer (or similar long pointy object) are the tools you need.