An atom has a nucleus that consists of neutrons and protons. Surrounding the nucleus are electrons that are orbiting the nucleus like the Earth orbits the Sun, just like above. This is called the Bohr’s model.
This is the simplified model everybody in school is given to work from and is a very good way to visualise it. Unfortunately the real story isn’t quite as simple. The real story looks more like this:
Its what we call an electron cloud. This is the area in which an electron can be found. The reason an electron cannot orbit the nucleus like the Earth orbits the Sun is because it would then be constantly accelerating. (Acceleration being a change in direction in this instance). Any object that is accelerating continuously emits electromagnetic radiation and loses energy. This means that the electron would quickly spiral into the nucleus and we know that this does not happen.
The reason Bohrs model is useful is because it helps us visualise the energy levels. So we do still use it in some cases. Its not completely null and void but the truth is that electrons can be anywhere at anytime. An electron that sits in the lowest energy level may actually be the furthest electron away from the nucleus but its more likely to be closer to the nucleus than the higher energy level electrons.