how to store something

You can use any capacitor. The voltage across a capacitor is a measure of the charge stored within the capacitor: V=Q/C
where
V=voltage
Q=charge
C=capacitance

Theoretically you can store charge in chunks as small as on electron. Practically, due to tolerances, you need a change of a few tens or hindreds of millivolts to reliably discern different charge states of the capacitor. But a few states (e.g. 0, 1/4, 1/2, 3/4 and full charge) should be storable in one capacitor making 2 bit in this example.

This is similar to how information is stored in a multilevel FLASH memory cell.