Lunar eclipses are caused because the Earth casts a shadow on the Moon, just like Solar eclipses are caused because the Moon casts a shadow on the Earth.

Lunar eclipses are possible only during full moons when the Moon, the Earth and the Sun line up with the Earth right in the middle blocking the Sun's rays from reaching the moon.

Here is an interesting quiz on Qalaxia for you to try that explains why we don't see a lunar eclipse whenever there's a full moon. Did you ever wonder about that?

https://www.qalaxia.com/quiz/599532987f362c661ac4e8b0