Difference between Voltage and Current

Before moving on to the circuits, we can first discuss the Difference between Voltage and Current.

VOLTAGE: Voltage is the potential difference between any two points of a circuit. potential is nothing but the capacity of an electron to do a work (work is nothing but the movement of charge). voltage is defined as work done (joules) per unit charge(coulomb), it is measured in volts.

1-volt = potential difference that forces 1-ampere of current through 1-ohm resistance.

CURRENT: Current is the rate flow of electrons through a conductor or a semiconductor. It is measured in Ampere(amps). 

1-ampere = flow of one coulomb of charge per second through a conductor or a semiconductor.

For example, we take a simple circuit

In this circuit an LED is powered by a battery, the current in the circuit is always measured in series in the circuit, since the current is the rate of flow of electrons. when the current flows through the ammeter current is measured, since ammeter has very low resistance, it does not affect the circuit very much.

Resistance - It is property of materials which resist the flow of current through them,

The component which only has a property of resistance is called a resistor.

The voltage is always measured in parallel across the required component, in the above circuit, the voltage is measured across the LED. since the voltage is the potential difference between the terminals of a circuit the voltmeter is always set parallel with the components, 

The voltage cannot be measured unless there is a potential difference, if the voltmeter is set in series there will not be any potential difference so voltmeter is useless in series and also it has a very high resistance it affects the circuit, and so it is kept parallel.

in the above circuit the current flows in the clockwise direction, and so the ammeter reads the positive value.

when the current enters the ammeter in the positive terminal and leaves at the negative terminal, the current value in the meter is always positive, when it happens vice versa the current value has a negative sign.

In voltmeter, the voltmeter shows positive value when the potential at the positive terminal is higher than the potential at the negative terminal, and it shows negative value when the negative terminal has higher potential than the potential at the positive terminal.