The North and South poles are the points on the Earth where the axis of rotation intersects the surface of the planet. They are the furthest points from the equator.
Because they are on the axis of rotation, the spin that gives the rest of the world day and night does not have the same effect at the poles. The orbit, not the spin, causes the sun to move up and down in the sky. The sun goes around and around in the sky at the North pole in Summer, and around in the sky at the South pole in Winter. The equinox is the only time the sun can be seen from both poles, and then, it is on the horizon. All the rest of the time, the sun shines on one pole and the other is in darkness. It reaches it's maximum altitude of about 23.5 degrees above the horizon at the solstice, the same as the angle between the equator and the ecliptic. The poles are cold because the sun never gets very high, so the sunlight (and radiant heat from the sun) is spread more thinly over a larger area.
Latitude is an angular measure of the distance between a point and the equator, colatitude is an angular measure of the distance between a point and the poles. The poles are at 90 degrees latitude, 0 degrees colatitude. The Tropics of Cancer and Capricorn are at 23.5 degrees latitude, (90 - 23.5) degrees = 66.5 degrees colatitude. The equator is 0 degrees latitude, 90 degrees colatitude.
The poles are the two places on the Earth where there is no longitude.