Almost everything has a computer or wires these days, here are some of the concepts and knowledge you will need to know to be able to test circuits and find electrical problems.
Voltage is displayed as a V or Volt. It is the measurement of the potential difference of electricity between 2 points. Think of a big rock up on a mountain just sitting up there. If you push that rock off the cliff it is going to roll all the way down the mountain until it hits the bottom, how high that mountain is above the ground below is a ‘potential difference’. Electricity works the same way as that big rock, but instead of measuring the height difference of the mountain to the ground in feet you are measuring the difference of electricity potential in Volts.
Electricity is similar to water in how it acts, if you go turn on your sink water comes out because there is ~40psi of water pressure in the pipes. The potential difference between the water in the pipe and the empty sink is ~40psi. A pressure washer may have a potential difference of 3000psi.
Current is displayed in A or I or Amps. It is the measurement of the flow of electricity. Think of the difference between a garden hose and a fire hose, even if they have the same water pressure the fire hose is going to fill up a bucket much faster than a garden hose.
Power is measured in P or W or Watts. Power is how much energy is actually used. You can calculate Watts by multiplying Volts x Amps. Lets use a road to explain this one, if you have a highway and you need to get more cars through that road how could you change it? If you increase the speed of the vehicles (volts) more cars would travel through during the same amount of time as before. You could also expand the road and add an additional lane and keep the speed limit the same as before, maybe for safety reasons you cannot increase the speed of the vehicles. A 1 lane road with a 100 mph speed limit and a 2 lane road with a 50 mph speed limit would in this example move the same number of cars.
Resistance is measured in ohms or displayed with this symbol – Ω. Resistance is a measurement of things trying to stop electricity from moving through it. Resistance will cause voltage to drop when electricity passes through it and usually will create heat as a result unless the resistance is so high that electricity cannot flow at all.