The Moon does not make its own light; the sun illuminates the Moon.
When a model is “to scale,” object sizes and distances are larger or smaller than in the real world but the same relative to one another. Some models need to be “not to scale” to be useful.
The sun illuminates the half of the Moon that is facing it, and the other half is dark.
Light from the sun travels in straight lines.
From Earth we can only see the half of the Moon that is facing us.
Because the Moon moves to different positions around Earth, we see different amounts of the illuminated half of the Moon. This is why we see different phases of the Moon.
There is a pattern to the position of the Moon because the Moon orbits around Earth.
It takes about one month for the Moon to orbit Earth, so it takes about one month to see the full pattern of moon phases. This pattern repeats with every orbit of the Moon.

Pick a key concept that you understand well and explain it in a way that an elementary school student could understand.