Imagine the an atom and an electron as planet earth and the moon. The difference is that an electron can move in every direction around the atom, in our comparison to the earth and the moon this would mean that you could see the moon in every position in the sky. Unlike the moon the electron moves much faster. For the most part the moon is at the same distance from earth just like the electron is at constant distance from the atom. But sometimes the moon can come a bit closer and then we get a so called supermoon, an electron can do the same and come closer to the atom.