The Moon reflects sunlight. The Sun normally lights half of it, and its orbit changes how much of that illuminated half we see. Near new Moon, the lit side mostly faces away from Earth. Near full Moon, the lit side faces Earth. Ordinary phases are not caused by Earth’s shadow.
A solar eclipse needs close Sun–Moon–Earth alignment, with the Moon’s shadow reaching Earth. A lunar eclipse needs Sun–Earth–Moon alignment, with Earth’s shadow falling on the Moon. Most new and full Moons do not cause eclipses because the Moon’s orbital plane is tilted. Never look directly at the Sun without appropriate certified protection.
Example 1
In the order Sun–Moon–Earth, which eclipse is possible if alignment is close enough?
A solar eclipse: the Moon can block sunlight from reaching a small part of Earth.
Example 2
Why is there not a lunar eclipse at every full Moon?
The Moon’s tilted orbit usually takes it above or below Earth’s shadow.
Watch out: Phases come from viewing different portions of the sunlit half. Earth’s shadow is involved in a lunar eclipse.