Quantum mechanics means dealing with physics at a very small level. Or u can say microscopic level. Studying physics at sub atomic level
Study regarding protons, electrons and quarks include in this study.
Also the laws of physics at normal level fail in quantum mechanics.
Laws like uncertainty principal of Heisenberg, wave nature, are there
(So if u want to write an essay, first u can tell about) the difference between normal sized objects and the subatomic ones. And how physics act upon them
Then u can write about how laws fail for microscopic things so we need to study quantum mechanics.
And elaborate every paragraph like i ve written in points.
hope that will make ur essay complete ♥