Some are only an inch or so across. The moon is made up of various kinds of rocks. These rocks are fairly similar to the rocks on earth. But on earth, we have wind and rain that help wear the rocks down into sand and dirt. There is no air or wind on the moon, so the rocks don't get worn down as they do on the earth.
Earth has only one moon.
The bright part of the moon is the part that the sun is shining on. This is like daytime on earth. The dark part is in shadow, like night on earth. At new moon, the moon and the sun are on the same side of Earth. We see the part of the moon that is in shadow, so the moon is dark.