There are five basic terms (to start with at least) in electrics/electronics and they all play a role in an electric guitar or bass:
Voltage
Current
Resistance (Impedance)
Capacitance
Inductance
Voltage (V), current(I) and resistance(R) for DC voltages are all tied together in a neat little equation called Ohm's law. V=IxR or I=V/R or R=V/I.
Resistance is a basic property of a material and indicates how well current (the movement of electric charge) will flow through that material. Most metals have a low resistance and conduct electricity well (though some still conduct electricity a bit better than others). So these metals are called conductors. Most plastics, wood and stone have a very high resistance indeed and won't conduct electricity (unless there is a very large voltage indeed placed across them) so these are called insulators. In between these two extremes are materials that will pass electricity, but not as readily or as much as a conductor will, and these are called resistors. When you move away from basic DC (direct current) circuits and into AC (alternating current circuits - basically any circuit that the voltage varies over time), the trem resistance is replaced with 'impedance' as the resistance value will depend of the frequency of the signal. So a piece of wire will have a different resistance value for a 10kHz signal compared to a 10MHz signal.
Voltage is a measure of the difference in electrical 'potential' across a circuit. You can compare it to a hydroelectric dam. When water is the same level both sides of the dam, there is no height difference to force water through the turbines and generate electricity. When there is no voltage present across a circuit, there is nothing to make any current flow, so nothing happens. When the dam is half full, there is now enough water pressure to make water flow through the turbine and generate some electricity, but not enough as when the dam is full, so there's maximum pressure available and the turbines produce their full power. So voltage is akin to the height difference between two sides of the dam (and indeed an older term for 'voltage' was 'pressure').
Current is a measure of how much electricity is flowing through an object, be it a conductor or resistor. The amount of current is always dependent on the voltage across that object and its resistance (and hence Ohm's law) We can't really control current directly, so we normally control it by adjusting the voltage or resistance of a circuit. So the primary form of Ohms law is really I=V/R, (though I more easily remember V=IxR).
Resistors are very useful, because in electronics, we normally want to limit or control the amount of current flowing through a circuit, or for a given current, control the voltage at a particular point in the circuit. So you get a huge range availble of fixed resistors, and also a wide number of potentiometers, which can be used as either 'variable resistors' (as in passive guitar tone controls) or as 'potential dividers', such as when used as guitar volume controls.
Going back to the dam analogy, the pipe the water passes through to get to the turbine can be compared to a conductor or low-value resistor/ A small pipe won't pass much water through it compared with a large pipe and can be said to have a relatively high resistance compared to the bigger pipe. The volume of water passing through the pipe is dependent of both the size of the pipe (smaller = more resistance) and the height of the water in the dam (more water = more voltage). So to increase the water flow (current) in the pipe we can either increase the height of the water in the dam (= more voltage), increase the size of the pipe (= lower resistance), or add a bit more water and a bit larger pipe size. Just like in electronics, we don't normally want all the water flowing out of the dam at once, so we pick the right resistance/pipe size to give us a good nominal water/current flow to drive the turbine (relevant part of the circuit).
A capacitor is a device for both storing electric charge, and also allowing an alternating current/AC (e.g. audio signal) to pass through it whilst blocking any direct current (DC) e.g. battery voltage, to pass through it. E.g. Large value capacitors are used in most power supplies providing a DC output, in order to store energy that's used when the AC input supply is at or near the zero voltage part of its cycle. Guitar amps and FX pedals will generally have one or more 'DC blocking' capacitors in the audio circuit to prevent and battery voltage or induced DC voltage from affecting the audio signal and giving a 'DC offset'. A DC offset can cause a speaker to have the wrong centre point, so that instead of vibrating back and forth as normal, it starts out near one end of its design travel length, and the normal audio vibrations cause the speaker to exceed its design travel, and can cause nasty audio distortion and speaker burnout. Capacitors basically work on an 'electrostatic' principle.
Capacitors can also act as simple filters on their own e.g. the tone control capacitor in your guitar when set to maximum roll-off, will pass the higher frequencies from the guitar signal to ground, but not the low ones, which is why the sound is muddy. The smaller the capacitance value, the higher the frequency point, above which the capacitor passes the signal, is.
Inductors work on electromagnetic induction and are basically coils of wire. By simply forming a wire into a coil, you turn it into an inductor, the more coils you have, the bigger the inductance will be. Put two coils together in the right way, and you get a transformer. Or wrap loads of turns of a thin wire around a former, add a magnet or two and you get a guitar pickup.
Resistance, capacitance and inductance are generally properties that all electrical items have, some on purpose and some dependent on the installation. So an inductor will also have a small amount of capacitance and some resistance.
Putting together resistance, capacitance and inductance in various combinations, you get different filter circuits, which can be low pass, high pass, band pass (or resonant versions of those).
The combination of a guitar pickup (with inductance, resistance and some capacitance), along with the resistance of the volume pot and the resistance+capacitor of tone circuit for a resonant low-pass filter, which helps shapes the sound of your pickup.
So a brief and very sketchy introduction to some of the basic terms, which are probably still confusing. Really best to look for a basic book on electronics. You won't need it all (and the maths for the frequency response circuits of capacitors and inductors gets complicated quickly as imaginary numbers are used), but I learnt this stuff ages ago, so really can't recommend a good basic book, but maybe others might. It really is useful, though not strictly necessary if you just follow wiring diagrams, in understanding how guitars and basses work and in fault-finding on them. Know the basics, and watching the YouTube tutorials on guitar filter circuits will make far more sense.
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