Quantum mechanics is about putting a particle in a box. People worry about where the particle goes. It cannot leave the box. So, people look for it. Heisenberg is uncertain where the particle is. I could explain why he can not find the particle, but I need calculus and big words to talk about it. I would also need to make many red links. Please forgive my red links and go read the Simple English Wiktionary.
Quantum mechanicians break the world down into whole numbers called "Quantum numbers". Things skip between one whole number and the next without ever falling in between. For example, electrons can be here or there, but not everywhere. Except for "spin", quantum numbers can not be fractions.
Many chemists and physicists like to study quantum mechanics. It makes them feel good about their understanding of nature. But all science articles written in Simple English are not allowed to talk about it.