A qubit can be represented by the spin of an electron or the polarization of a photon.
Related: Electron spin, Photon polarization, Quantum Computing for Everyone
Just like a bit can be represented by any device containing two distinct states, e.g. switch, coin, etc. a Qubit can be represented by anything that can be in two distinctive states as well as a combination of those two states. Therefore, the Electron spin or the Photon polarization are some of the ways to represent a qubit.1