This is meant to be a basic introduction to electricity / electrical concepts for those who have limited or no electrical background.
V = Voltage (measured in volts V)
I = Current (measured in amps A)
R = Resistance (measured in ohms Ω)
The above equation is Ohm’s law and should get you through most of what you need to know. In terms of an analogy, if electricity is like water flow, then voltage would be like pressure (differential), current like flow and resistance like the size of pipe. In practical terms, resistance is probably determined for you and the thing you have most control of is likely voltage.
Everything has resistance, just a matter of how little or how much. Something with low resistance (low ohms) will allow electricity to flow more freely than something with high resistance (high ohms). To go with the water flow analogy, resistance is like size of pipe. A larger pipe will have lower resistance allowing higher flow while a smaller pipe will have higher resistance restricting flow.
Voltage is the potential difference between two points. In order for electricity to flow, there needs to be a difference in voltage between two points. When measuring battery voltage with a multimeter, you need to put one probe on the positive terminal and one probe on the negative terminal. If you place both probes on the same terminal, you’ll see 0 volts. The higher the voltage (volts), the more dangerous something is and the further you should stay away. Like differential pressure, the higher the pressure (voltage), the more flow (current) it will allow up to a certain point – determined by pipe size (resistance).
Current is the flow of electricity measured in amps (amperes). For practical intents and purposes, current is the result of adjusting voltage given a fixed resistance. In the water flow analogy, current (flow) is the end result of changing the pressure (voltage) by opening or closing a valve like a faucet that’s connected to a hose (resistance). If you want to increase flow, you don’t start by changing out the hose, you go and turn the knob to increase pressure. But at some point, if you have a tiny hose hooked up to a fire hydrant, the flow and pressure will cause the hose to fail. Electrical current is somewhat like that, you can increase current by increasing voltage and too much current on a given wire will destroy it.
If we rearrange the equation for current, we see that as resistance gets bigger (dividing by a larger number), current decreases and as resistance gets smaller (dividing by a smaller number), current increases. This equation (Ohm’s law) is very useful when looking at the relationship between the basic components of electricity, if any of these things go to 0, the whole thing just doesn’t work and there’s no electricity flowing. For example, as resistance gets towards 0, current increases, if you connect positive terminal to negative terminal directly without any load in between, you’ll have a short circuit and a lot of current flowing. Things will heat up and fail, some times in spectacular fashion.
You can break things by supplying too much voltage and you can also break things by having too much current. The two are related and increasing voltage will increase current as well given a fixed resistance.