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You've got that pretty much right, DJV.
The meridian is simply a line drawn between the north and south celestial poles and which passes through the point directly above the observer (you). That point is called the zenith.
We in the southern hemisphere cannot see the north celestial pole so we have to work out where it is, even though it's below the horizon. While it sounds hard, it's not. Drawing an imaginary line between the south celestial pole and the point directly above you and then extending the line to the northern horizon shows you the direction of the north celestial pole.
Now the poles: Firstly, ignore the tilt of the Earth relative to the Sun. The Earth, in a general sense, is static relative to the stars - other than its spinning around once a day. This means that the stars (not the Sun or its planets) trundle around the sky as we see it on a regular basis and pretty much in the same position. Because the Earth does spin and because the Earth does do a lap of the Sun once a year it means that the stars appear to move in the sky when seen from any point on the planet. As a result of this the poles - which you correctly describe as being points extended from the north and south poles of the Earth - do not appear to move. They do, but not noticeably, as the Earth 'wobbles' a bit. This is known as 'precession' but it takes some 20 odd thousand years to complete a circuit and is ignorable in most peoples' lifetimes.
Should you have difficulty with the concept then temporarily turn yourself into a 'flat earth' believer, but with a twist. Imagine Earth being a disc with some of us living on one side and the rest on the other. Assuming that said disc did not move relative to the stars then observers on one side of the disc would not see the same stars as those on the other side.
Of course the Earth is a sphere, so the point from which you observe the sky will (and does) affect what you can see and where you see it.
Blimey, I hope that makes some sort of sense.
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