Sometimes in the afternoon I see the Moon.
Why is this?

The Moon is going around the Earth in a big circle all the time. We can see it only when it is up above our side of the Earth. And we see it because of the light that falls on it from the Sun.

When the Moon is up above us at night, it seems to glow brightly because of the dark sky behind it. When it is up above us during the day it glows just as brightly. But then the sky behind it is so bright that we usually do not even notice it. You must have been looking carefully to see it in the afternoon.