Celestial Navigation Devices take you back to the sailing of old. It’s a trip through time back to when sailors would use such instruments to determine their position when they were far out at sea and there was no land in sight. The way they work is to use the angle between a star (or our star, the Sun) and the horizon. With this you can then find out where you are, which is your celestial geographic position.
In order to make use of a Celestial Navigation Device, you need to have an accurate idea of where certain stars will be throughout the year. Astronomers can create an Almanac (an astrological calendar) which will tell you where stars will be at a given hour or even minute. Alternatively you can use the North Star, which always rests 90 degrees above the North Pole.
The other thing you will need is a watch, which today is no big deal but accurately telling the time was a real issue to the sailors of old.
Finally you need an angle measurement device. Below shows how a Sextant works. Simply by lining up the celestial body with the horizon will allow you to determine your position. Then the more stars you line up the more precise you can be about your position.
“Using sextant swing” CC Joaquim Alves Gaspar (to watch the gif file click View in browser)
Watch this informational video to get a better understanding of the basics of using a sextant.