There are two types of eclipses, solar and lunar. They are similar in how they happen, but the effects are very different.
Solar eclipses happen when the moon is between the sun and the earth, and everything lines up so that the moon's shadow goes onto the earth.
Lunar eclipses happen when the earth is between the sun and the moon, and the earth's shadow falls on the moon. The moon will turn a blood red color during a lunar eclipse.