Do you mean the full moon, etc? Earth blocks part of the light from the sun, causing the moon to be partially visible. The moon reflects light from the sun that we can see easily at night in the areas not blocked by Earth.
The moon has phases that are not due to the shadow of the earth. As it revolves around the earth, the portion of moon that is in light keeps on changing. The moon takes 27.3 days to go around the earth, but the phase cycle of the moon, ranging from full moon to new moon, takes 29.5 days. The new moon is the result of the shadow of the earth that falls on the moon, but the phases of the moon are not due to the earth’s shadow, but due to the arrangement and orientation of the moon and sun in the sky.