Why does the Moon always show us the same face?

Because it rotates exactly once per orbit - so it is turning, just at the rate that keeps one side towards us. That is tidal locking, and it is not a coincidence: Earth's gravity raised a bulge on the Moon, and the pull on that bulge acted as a brake until the rotation matched the orbit and the bulge stopped moving.

We actually see about 59 per cent of the surface, not half. The Moon's orbit is elliptical and tilted, so it appears to rock slightly north-south and east-west over a month, letting us peer a little way round each edge. The effect is called libration, and it means a strip around the limb comes and goes.

There is no dark side. The far side gets exactly as much sunlight, on the same monthly cycle - it is the far side, not the dark one, and it was first seen when a Soviet probe photographed it in 1959. It looks strikingly different, with almost none of the dark volcanic plains that make the near side's face, and why the two hemispheres differ so much is still argued about. The same locking is happening to Earth: our day lengthens by roughly two milliseconds a century.