What is quantum mechanics? Quantum mechanics is the leading cause of cat death, and also not the leading cause of cat death.
If a (lame) joke like that goes over your head, then you definitely need this list. Quantum mechanics reveals a fascinating set of physical laws and theories that explore such questions as "Wait, is the universe really made of string?" "Yo, dawg, what about time travel?" and everything in between. And everything inside. And around. And invisible. Don't worry if it all sounds confusing - it's only, like, the laws of nature and everything as we both know and don't know it. No big deal at all!
The good news is that we're all in this together. Come along on a journey through space and time (if you read that in the voice of Neil deGrasse Tyson, you are correct) to learn some quantum mechanics facts. Why, by the end of this quantum mechanics overview, you'll likely be able to deliver an explanation of quantum mechanics and a robust litany of quantum theory facts to your cat. Just, uh, leave the feline-themed experiments to Schrödinger.