The Moon, like the Sun, the Earth and the other planets, is a big round object in space. Sometimes it might not look round. It might look like a semicircle or a crescent in the sky, but that’s just because the Earth’s shadow covers part of it. When there’s a full moon, we see the Moon’s full shape, a sphere.
The moon got its shape because of gravity. It has gravity just like the Earth does. Gravity pulls everything to the center of a big object. That’s why we don’t float off into space. The Earth is pulling us to its center!
The Moon may have started out as a weird and irregular shape or as a bunch of floating chunks of rocks, but over time, gravity collected it, pulling and tugging the rocks that make up the Moon together until they were collected into a neat, round ball.