A regular computer stores information as bits that are either 0 or 1. A quantum computer uses qubits, which can exist in a combination of both states at once — a property called superposition — and can be linked together in ways that let the machine explore many possible solutions to a problem simultaneously.
This doesn't make quantum computers faster at everyday tasks like browsing the web or editing a document. Their advantage shows up in a narrow set of problems — certain kinds of optimization, simulating molecules for drug discovery, and breaking specific types of encryption — where the quantum approach scales far better than any classical algorithm we know of.
Today's quantum computers are still small, error-prone, and mostly confined to research labs and specialized cloud services. Useful, large-scale quantum computing is generally viewed as still years away, but the field is progressing steadily on error correction, which is the main blocker to real-world scale.