It's an incident meter. I verfiry ISO is set correctly and aim it in the opposite direction as the camera. Within 30 degrees aim is good enough. I press the button to take a reading. The needle moves to it's position, and I spin the dial so the other needle matches and I get all my aperture/shutter combinations.
I assume the same applies when using its reflective metering function. Obviously it'll take some practice to get it right.