What Is Superposition?
Myth: A qubit is 0 and 1 at the same time, or, secretly one or the other, we just don't know which yet.
Reality: Neither. It's a distinct physical state (a weighted combination of both) that only becomes a definite 0 or 1 once measured.
Two common explanations of superposition are both a little off. "The qubit is 0 and 1 at the same time" oversells it: you'll never observe a qubit reading out "0 and 1" together; a measurement always gives you exactly one definite answer. "The qubit is secretly 0 or 1, we just don't know which yet" undersells it: that's how a classical coin under your hand works, and it doesn't match what experiments actually show quantum systems doing (interference effects that only make sense if the "unknown" possibilities were all genuinely contributing beforehand).
The accurate description is mathematical: a qubit's state is a weighted combination, technically a linear combination with complex-number weights called amplitudes, of the "0" state and the "1" state. Those amplitudes determine the probability of measuring 0 versus 1, and (this is the part everyday language has no good word for) they can also interfere with each other, the way overlapping waves can amplify or cancel. That interference is the actual resource quantum algorithms exploit; it's the reason superposition matters computationally, not just a curiosity about "being in two states."
Superposition by itself, on a single qubit, is fairly limited. Its real power shows up once you combine it with entanglement across many qubits, which is where the state space genuinely outgrows anything classical bits can represent efficiently.
Put a qubit into superposition yourself and watch it on the Bloch sphere in F1 — Quantum States.