Is when the moon's shadow appears on the earth surface, a solar eclipses is occurring. As earth rotates, moon's shadow moves along earths surface.
Total Solar Eclipses
You can only see one from within the moons umbra.
During a solar eclipse the moon appears to cover the sun completely.
This Eclipse last no longer then 7 min.
Partial Solar Eclipse
See a particle Solar Eclipse from within the Moon's much larger penumbra.
The moon never completely covers the sun.
Why do eclipse not occur every month?
Only during a new moon, solar eclipse occur. But they don't occur during every new moon phase. Moons orbit is tilted slightly compared to earth's orbit.
Occurs when the moon moves into earths shadow.
They can only occur during the full moon phase.