If you aren't near any of the cities on the list, you can still use the Sun Clock. Go out at night and look for the North Star. Mark an arrow on the ground that points toward the North Star. That's geographic north. Now follow the rest of the instructions on the diagram.
Shadows change direction, depending upon the time of day.
A Sun Clock like this one uses a shadow's position to tell the time. The time you get from your Sun Clock is solar time, not standard time. The two aren't exactly the same. According to solar time, it's noon when the sun reaches its highest point in the sky. Back before 1883, people used solar time.