Current, Power, Resistance & Voltage

Current is measured in amps (a), symbol: i.
It is a measure the amount of electricity that can flow in the circuit.
If electricity was water in a hosepipe, current would be the width of the pipe*

Voltage is measured in Volts (v), symbol; v.
It is a measure of how much 'pressure' is available to push the electricity around.
Think of a water tank up in the air, connected to our hose.
The greater the pressure (ie. height), the faster the water will flow in the hose.

Resistance is measured in Ohms (Ω), symbol; R.
It is a a measure of how difficult (or easy) it is for the electricity to flow.
Increase the resistance? Think of squeezing the end of the hosepipe...

These three are interrelated by the equation V = i R
Or: Voltage (in volts) is Current (in amps) x Resistance (in ohms)
This can be re-arranged as i = V/R, and also R = V/i. This is Ohm's Law.

Power is measured in watts (w), symbol; P.
Power is a measure of the amount of electricity used in a circuit.
Think of the bucket filling up with water. It's a measure of how much water has flowed.
Power (the amount of electricity that flows) is a product of how much electricity can flow (the current) and how much pressure is being exerted (the voltage).

So Power = Current x Voltage, or   P = i V.

If we mant to get fancy, we know that v = i R, so we can swap the v for i R...
To give us another formula:   P = i i R   better written   P = i ² R

As far as DC electrics goes, that'll be more or less all you'll need to know, unless you want to get really technical, and even then the maths is just more complicated but in the same vein. Pertinent questions will help to direct further explanations.

*Actually it'd be cross-sectional area, but let's keep the metaphors simple...