Polaris or the Northern Star marks the North Celestial Pole, and has been very useful for determining latitude throughout maritime history in the northern hemisphere. Part of the Ursa Minor constellation, Polaris is fairly visible, even with simple telescopes, while its position in the sky barely changes. The star's elevation above the horizon reflects the observer's latitude. The use of a sextant, which is an instrument to measure the angle between a celestial body and the horizon, is necessary to know the exact latitude by observation of Polaris.
The Crux or the Southern Cross is a small constellation only visible in the southern sky. Like the northern hemisphere, the southern hemisphere also has a star sitting almost exactly at the pole, but it is quite hard to find it. However, observing the Southern Cross is the easiest way to find the south. By simply extending the long axis of the Cross from the bottom star by four and half times its length. That point indicates the south celestial pole.
Determining the west and the east by observing the sun's location in the sky is simple, especially at times close to dawn and dusk. Point your right arm to the direction where the sun has raised. That is east. You then have the south to your back, west to your left and north to your front.