You must understand the concept and unit of each term accurately so as not to make mistakes in the basics.

1. Voltage (V)

It refers to the potential difference between two points and is the force that causes current to flow.
Conceptually, when there are water tanks A and B in the figure below, the difference in the water levels of the two water tanks is
You can think of it as voltage. If the water level in water tank A is high, water tank B
The amount of pressure received increases.
As the voltage increases, the power of the flowing electricity also increases.
The unit is Volt and the symbol is “V” or “mV”. (1V=1000mV)
So how much power is 1V?
1V is the pressure that can produce 1A of charge.
1V is equivalent to 1W of work
Here, watt (W) is a unit of electrical power, or electric power.
Power is measured in watts (W) or kilowatts (kW), with 1 W being the amount of current that flows when 1 A ( ampere ) flows across a voltage of 1 V ( volt ).
The amount of power consumed.

1W=1J/s

1J is the work required to move an object of 1 Newton a distance of 1 meter.
Also, 1 N is the force required to move an object with a mass of 1 kg at 1 meter per second.

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2. Current (I)

Current is the amount of charge flowing through a conductor.
The unit of charge of an electron is the Coulomb, and 1 Coulomb (C) is the charge carried by 6.25x10 ¹⁸ (625 quadrillion) electrons.
The unit of current is expressed using a unit called ampere (A) . (1A = 1000mA)
1A means that 1 coulomb of charge flows per second.

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3. Resistance (R)

Electric current is the flow of free electrons, and when free electrons move, they are hindered by the attraction of the atomic nucleus and the repulsion of other free electrons. This hindrance to the flow of current is called resistance, and all materials, including conductors, have resistance. A material that has low resistance and through which electricity flows easily is called a conductor, a material that has high resistance and through which electricity does not flow easily is called an insulator, and the area in between is called a semiconductor.

A material whose resistance is close to “0” is called a superconductor.

The higher the voltage, the more current, and the lower the resistance, the greater the electric power.
The unit of resistance is "Ohm" (symbol Ω).
When a voltage of 1 V is applied and a current of 1 A flows, the resistance is called 1 Ω, 1000 Ω is called 1 kΩ (kilo ohm), and 1000 kΩ is called 1 MΩ (mega ohm).

In electronic circuits, resistor elements are used according to the allowable current of the component being used.

As shown in the figure below, the nature of resistance is such that when the material is the same, the larger the cross-sectional area, the smaller the resistance. The longer the length, the greater the resistance. Therefore, resistance varies depending on the type of material (because the atomic structure is different) and has a value that is inversely proportional to the thickness of the wire and proportional to the length of the wire.

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The table below is the American wire size chart, and the wire diameter is the diameter excluding the outer sheath.
When the line length is long, resistance and allowable current must be considered.
In electronic circuits, AWG24 to AWG28 are commonly used.