If you stand outside on a clear night, you will see half of the celestial sphere above you. Surrounding you is the circle of your horizon - it is a plane and you are in the centre of it. Directly above you is your zenith; directly below you is your nadir.
Turn to face directly north. Imagine a semicircle arcing above you, drawn south to north, passing through your zenith, with you in the centre facing the north end. This is your meridian. A line drawn between the points where it meets the horizon would go north-south; a line perpendicular to that east-west. Everyone on the same longitude has the same meridian. The prime meridian at 0° is at Greenwich in London.
If you were at the north pole, the stars would appear to be rotating in concentric circles around a fixed point right above you. This is where the earth’s axis is pointing: the earth rotates around this axis, and so the stars appear to rotate around it, too (in the other direction.) These stars, while you’re at the north pole, are circumpolar - they do not sink below the horizon.
If you moved downwards into Russia (for example), you would no longer be at the centre of everything. Facing north, the north pole is forwards. So the fixed point that the stars rotate around has “moved” forwards, too. It’ll be at an angle in front of you - although still quite high up. And now, because the fixed point has moved downwards, all the stars have, too - and you can’t see the bottom of the largest circles anymore. Those stars are completing their circling below your horizon. They are no longer circumpolar - most of the stars still are, though.
Now of course you’re not going to see the full circle - because half of it takes place in daylight! What I mean, though, is that it takes place within your area of vision. (Ignore night and day for the moment.)
The further you move towards the equator, the more that fixed point moves downward, and the fewer stars are circumpolar. Eventually, you’ll get to the equator. You’ve moved 90° around the earth - and so the fixed point has gone down 90° from right above you. That means it’s now right on the horizon. You can’t see below your horizon - that means that half of each circle is out of sight. None of the stars are circumpolar at all.
When a star reaches its highest point in its circle, this is its upper transit. At its lowest point, it’s the lower transit. You can see all of the upper transits - but not all of the lower transits, unless you’re right at the pole. When the star has completed two transits, it’s rotated once around the axis (or rather, the earth has). This takes about a day.
After its upper transit, the star culminates. The celestial equator surrounds the earth's equator, just further out.
Any change in a star's position relative to its neighbours is its proper motion. The star that shows the most proper motion is Barnard's Star, but it's less than 1/3° per century.