you use a teloscope
The brightest star among the other stars in the night sky is called pole star.
None. You're thinking of the star at the end of the 'handle' of the Little Dipper. That's 'Polaris', also called the 'North Star'. It's very close to the north pole of the sky, which is the point in the sky that everything appears to rotate around. That's simply the point in the sky that the earth's North Pole points to.
The pole star
The North Star is close to the north pole of the sky - one of the centers of rotation - of the apparent rotation of the sky around us (the other is the south pole).
The northern pole star "Polaris" is visible in the sky to an observer located anywhere on earth between the equator and the north pole, i.e. anywhere with a north latitude. There is no similar southern pole star.
Directly overhead.
No. Sigma Octans is a star close to the south pole of the sky, but it is not particularly bright.
The Pole Star appears to be stationary in the Northern sky, while other stars move in a circular orbit as the earth rotates. Once the Pole Star is found, people can use the pole to navigate should a compass is not available.
It is not the brightest star in the sky, as many people think. It's important because it marks, roughly, the "North Pole of the sky".
This is Polaris, often also called the north star or the pole star.
In Hindu mythology, Dhruva is considered the god associated with the pole star. He is believed to be a devotee of Lord Vishnu who earned a celestial place in the sky near the pole star due to his unwavering devotion to the deity.
It is purely coincidental that the north star Polaris happens to be fairly close to the north celestial pole in the skies. In fact, the Earth's rotation wobbles very slowly - called "precession" - over a span of 25,800 years. In about 3000 years, the north pole won't be pointing to Polaris, but to some other spot in the sky, and there will not be a "pole star". In about 12,000 years, the "pole star" will be Vega, and in 24,000 years it will be back to Polaris again. Because the precession is so slow, no human lives long enough to notice any changes.