What is an eclipse?
When the Sun, Earth and Moon line up exactly, one casts a shadow on the other.
In a solar eclipse the Moon passes in front of the Sun. By an amazing coincidence the Sun is 400 times bigger than the Moon but also 400 times farther away, so they look the same size.
In a lunar eclipse the full Moon passes through Earth's shadow and turns coppery red, lit only by all the sunsets happening around the Earth at that moment.
We don't get eclipses every month because the Moon's orbit is tilted about 5° to ours.