A lunar eclipse happens when the Earth passes between the moon and the sun. Lunar eclipses cast a shadow on the moon due to the Earth's location. From the perspective of the moon, the Earth completely blocks the sun.
According to MrEclipse, there are roughly 1 1/2 full lunar eclipses each year, although the number can be as low as zero or as high as three. There are both full and partial eclipses each year, and there are usually many more partial lunar eclipses per year than full. The angle of the moon's orbit makes it impossible for there to be full or partial lunar eclipses every lunar month.
The shadow of a lunar eclipse does not typically completely black out the moon. The moon is still visible even during full lunar eclipses, but its color changes, and it is less visible than it is before and after the event.
It is also much easier to see a lunar eclipse than a solar eclipse due to how close the moon and Earth are to one another. It is safe to view a lunar eclipse since the light from the moon can not damage a person's eyesight like the sun can, even during a solar eclipse.