Within a capacitor, three components are universal. Two of those components will be an electrical conductor. The third component is an insulator of some sort. The conductors and the insulator can be most anything, the metal foil is quite often employed as the conductor. In these designs, though metal foil is typically separated by a very thin layer of an insulating material.
When power is run through the capacitor, it generates a potential difference across the two conductors in the component. This creates an electric field across the insulator. The capacitor eventually stores the positive charge on one of the electrically conductive plates and the negative charge on the other electrically conductive plate. This allows energy to be stored in the form of an electrostatic field. The charges on each of the conducting surfaces are equal and opposite of the other. The charge on each of the conductors is measured as a coulomb and, combined with the voltage across the device, the capacitance of the device is measured in farads.