If you've lived here on planet Earth for very long, you've no doubt noticed that we have a Moon (a smaller rocky body, orbiting around the Earth).
Like the Sun, the Moon rises in the east, ascends slowly through the sky, and then sets in the west.
The Moon can appear during the day, but at other times is visible only at night.
Sometimes it looks like a thin crescent, slowly growing into a round, full circle over time. It takes about two weeks to grow from a thin shard into a full circle, and another two weeks to shrink down into nothing again.