Both digital and analog components
Voltage is the electrical potential. It is similar to water pressure in a pipe. Voltage is polarized, and relative, therefore it is often measured with respect to the earth, or ground. A parallel circut always has the same voltage across all components.
Current is the flow of electricity. It is similar to water flow in a pipe. Current is not polarized, and not relative. A series circut always has the same current across all components.
These two are related via the following equation (Ohms law):
V = I * R
Where V is voltage (Volts), I is current(Amps), and R is resistance(Ohms).
Power is Voltage times Current and is measured in Watts (W). Power is a rate upon which electrical energy is used.