Here's a breakdown:

* Electron Shells: These are regions of space surrounding the nucleus where electrons are likely to be found. They are organized into distinct energy levels, with the lower shells being closer to the nucleus and having lower energy.

* Energy Levels: These represent the different amounts of energy that electrons can possess within an atom. Electrons in higher energy levels are further from the nucleus and have more energy.

Think of it like a ladder:

* The nucleus is like the base of the ladder.

* The electron shells are like the rungs of the ladder.

* The higher the rung, the further away from the base (nucleus) it is and the more energy an electron on that rung has.

Electrons can move between these shells by absorbing or releasing energy, but they can only occupy specific energy levels. This arrangement is crucial for understanding how atoms interact with each other and form molecules.