The Moon's role
The moon is useful for eclipses, tides, and moon phases. This picture is showing the kinds of moon phases. Earth is the planet that has the moon.
Moon phases are changing relative positions of the moon, Earth, and sun. The moon has 8 different kinds of moon phases. There is new moon, full moon, first and third quarter, waning and waxing crescent and Gibbous. Most of the moon phases occurs at least once a month.