The Moon shines because its surface reflects light from the sun

 The Moon shines because its surface reflects light from the sun. And despite the fact that it sometimes seems to shine very brightly, the moon reflects only between 3 and 12 percent of the sunlight that hits it.

The perceived brightness of the moon from Earth depends on where the moon is in its orbit around the planet. The moon travels once around Earth every 29.5 days, and during its journey, it's lit from varying angles by the sun.

This movement of the moon around the Earth - and the simultaneous orbiting of Earth around the sun - accounts for the moon's different phases (full moon, quarter moon, etc.). At any given point in the moon's trajectory around the Earth, only half of its surface is facing the sun, and therefore, only half of the moon is lit up. The other half of the surface faces away from the sun and is in shadow.