How do you navigate by stars?

find the big dipper. its bottom of the cup will point to the north star. look straight up. draw an imaginary line in the sky from where your looking at to the north star. that is north.

Look for the star that doesn't appear to move in the sky, and looks like all the other stars are rotating around it. This is the north star. Following the North star leads you north.

because it's directly above the north pole so doesn't appear to move unlike all other stars and be used as a reference point to find other constellations

In the northern hemisphere you can find north by identifying the north star, Polaris. With appropriate equipment you can measure its apparent altitude over the horizon, thus giving you your longitude.

Because they travel at a constant rate across the sky. Additionally, Polaris (the north star) doesn't move at all - so it's a good reference point.