
The comment I am replying to, your comment in the tree, and the one next to you, does not seem to match that request in any sense.
Now, simplified definitions are an art, but Feynman managed it with Quantum Electrodynamics -- so it is not impossible to do it for complex subjects. And it seems to me the less you understand a subject, the less simple and more confusing your explanation will be, such as the explanations given by the other posters here. (fyi: I do not understand enough to properly convey my understanding clearly -- which is why I have not attempted to do so)
Quantum Electrodynamics (Feynman): A summary of how almost EVERYTHING works (albeit explained simplistically).
Poor Charlie's Almanack: The Wit and Wisdom of Charles T. Munger (great insights / worldly wisdom from one of the world’s greatest investors).
The Vital Question: Energy, Evolution, and the Origins of Complex Life
The Princeton Companion to Mathematics (Great overview of mathematics).
Quantum Mechanics: Concepts and Applications (Great QM book).
Wooden on Leadership: How to Create a Winning Organization (Great leadership / management insights).
Why Does the World Exist?: An Existential Detective Story
Sapiens: A Brief History of Humankind (An extremely simplified historical overview of how we got here).
The Book of Disquiet (Serpent's Tail Classics) (Random journaling from one of the world’s greatest prose writers: Fernando Pessoa).
Code: The Hidden Language of Computer Hardware and Software (Excellent explanation on how computers work from bottom -> top).
The Machinery of Life (Includes excellent visuals in biology).
The Character of Physical Law (Great insights in physics by Feynman).
The Goal: A Process of Ongoing Improvement (Great book on business process improvement).
How to Win Friends & Influence People (Nothing groundbreaking, but still a worthy read).
Coders at Work: Reflections on the Craft of Programming (Great info and insights from some of the greatest software developers of all time).
The Periodic Table (Great read and some of the greatest prose writing you’ll ever encounter).
Have you ever read the book QED? It's Feynman's best effort to explain Quantum Electrodynamics to a layman. In the book, he takes a genuine question about the nature of things (how does light work?) and answers it by "bringing up paper and arrows!" (I encourage you to read the book to see what I mean). Feynman disliked "explaining" nature with inaccurate and irresponsible metaphors. But arrows are the way it really is!
In fact, "trying all possibilities at the same time" is a ubiquitous phenomenon in Nature. Light rays find their trajectory by tryin out all possible paths and only the one with the highest constructive interference survives (this is what Feynman discovered in Quantum Electrodynamics, which is referenced in the article).
The real trick in quantum computing is manipulating qubits through quantum gates such that the outcome that gets assigned the highest probability is the correct one. This is indeed hard as the environment usually interferes and spreads out the probabilities across all outcomes, leading to a junky, random outcome.