this is the basic math, if you know these formulas you can find any of the values ...


E
-----
I * R

P
-----
I * E


E= Voltage
I= Current (amperage)
P= Wattage
R= Resistance

in an electrical circuit diagram they'll be represented like this:
Volts = V
current/amps = A
resistance = R / the ohm symbol
Watts = P




In a series circuit Amps(I) are always constant.
In a parallel circuit Voltage(E) is always constant.