Is there a dark side of the Moon and what is tidal locking?

Actually there is no dark side of the Moon, but from the Earth you can only see one side of the Moon. Thats because time it takes for the Moon to rotate one complete turn around the Earth is equals to time it takes for the Moon to rotate one complete turn around its axis.

As seen here.

Why is the Moons rotation so perfectly aligned?

That rotation alignement is not an accident and its not rare. Most of moons of other planets are tidally locked just like our Moon.

Tidal locking is happening because of tidal forces. Earths gravitation is deforming the Moon into an ellipse, the same way the Moon forms tides on the Earth. That phenomenon will be explained in my next post.

If the Moon is rotating faster around its axis (picture 1), the front of the bulge is turning upwards (on the picture below) and point A is pulled more towards the Earth than point B because its closer to the Earth, slowing the rotation of the Moon. If the Moon was rotating slower (picture 2) the front of the bulge would be turning downwards and again point A would be pulled more than point B and the rotation would be getting faster.

On real scales bulge is very small, but still big enough for tidal locking to happen.

Why isn't then the Earth tidally locked with the Sun?

To explain this I need to bring up some math. This is the formula for calculating the time it takes for tidal locking to happen.
We are only interested in variable a. Variable a is distance between two bodies. a is to the power of six, which means if distance gets 10 times bigger, the time it takes for tidal locking to take place gets 1000000 times bigger.
Which means it would take the Earth a lot more time to tidal lock with the Sun.
All of the Trappist 1's planets are tidally locked with the star because they are a lot closer to it than the Earth is to the Sun.