Just as classical computing is based on classical physics, quantum computing is based on quantum physics: it exploits the "weirdness" of quantum physics (its probabilistic nature, and the phenomena of superposition and entanglement) to create machines far more powerful than the ones we're used to using in everyday life. Quantum computers won't be just faster than even the most advanced of classical computers, they will work in a fundamentally different way - and will therefore be capable of tackling complex computing tasks that aren't even conceivable for existing machines.