The Sun is always in the same place in the sky, but the Earth is rotating. When it's nighttime in one part of the Earth, that part of the Earth is facing away from the Sun.

Think of it like this:

* The Sun is like a giant light bulb.

* The Earth is like a spinning ball.

When one side of the Earth faces the Sun, it's daytime. When that side rotates away from the Sun, it's nighttime.

So, to answer your question directly, the Sun is still in the same place when it's nighttime on Earth. It's just that the part of the Earth where it's nighttime is facing away from the Sun.