Question

why does the moon changes it's shape

Answer 1

The Moon appears to change shape because we see different amounts of the lit part as the Moonorbits Earth. When the Moon is between Earth and the Sun, the lit side is hidden from us. As it moves around Earth, more and more of the lit side comes into view. Then it begins to disappear again.

Answer 2

When Earth revoles around the sun, according to the light of the sun seeing the moon. so the moon changes its shape.