A full moon occurs when the moon appears as a full circle in the sky. We see it as a complete sphere because every side of the Moon facing the Earth is illuminated by the sun's rays.
full moon app
The full Moon does not produce visible light on its own, so we can only see which parts of the full Moon are lit by other things.

A small amount of light comes from distant stars and the reflection of light from Earth (known as "Earthshine"). But the main source of light for the full
moon is the sun.
The full moon appears differently in the sky depending on its "phase", from new moon to full moon via the "wax" (growth) and "reclining" (deflation) moons. These phases are determined by the relative positions of the Sun, Earth, and Moon.