An Electric Circuit is a interconnection of circuit elements. There are two things that are important

An Electric Circuit is defined as the path in which electrons flow from a voltage or current source. The point where electrons starts flowing is called source and where the electrons leave the circuit is called ground (or earthed). Lets go through a simple electric circuit,
The diagram using has electric
components to describe an electrical circuit like source S and resistance R.
To begin with electric circuit theory there are many electric components such as any lamp, a heater, a key, a wire etc connected to a battery that acts as source in such a way that the electrons flow ends to some point known as ground.
The electrical circuits are of two types :  Open circuit
 Closed circuit
Open
electrical circuit is that where the electric current does
not flow because the key is open or the switch is off whereas closed electrical
circuit is the circuit in which the electric current flows because the
key is closed or switch is on.
Its known that current flows in a conductor when a potential difference is maintained across its ends. How much it is? was a question.This was given by German scientist Simon Ohm, by his experiments who found a relationship between the potential difference and current in a conductor. This relationship is known as Ohmâ€™s law.
Ohm's Law states as,
The current that flows through the conductor varies directly to the potential across its ends if temperature and other physical conditions are kept constant.
If V is the voltage applied across the ends of a conductor then the current flowing through it is given by,
V = voltage applied across its ends
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Ohm's Law states as,
The current that flows through the conductor varies directly to the potential across its ends if temperature and other physical conditions are kept constant.
I = $\frac{V}{R}$
Where, V = voltage applied across its ends
I is current flow
R is resistance offered by conductor.
It was given by Gustav R. Kirchhoff, a German physicist discovered the principle of the voltage law also known as Kirchhoff Second Law (KVL) which states that "The algebraic sum of the voltage (potential) differences in any loop must equal zero".
It is given as,V_{1} + V_{2} + V_{3} + V_{4} = 0
$\sum$ V = 0
$\sum$ V = 0
Look at the below circuit
By KCL, we have
$i_{1}$ + $i_{2}$ + $i_{4}$ = $i_{3}$ + $i_{5}$
Electric charge is never accumulated at any point in a circuit .The algebraic sum of electric currents at a junction in a circuit is zero .
$i_{1}$ + $i_{2}$  $i_{3}$ + $i_{4}$  $i_{5}$ = 0
This is known as Kirchhoff's Current law.Lets go through same samples problems:
Solved Examples
Question 1: A 10 $\Omega$ resistor is connected across 10 V battery. Calculate the amount of current flowing through it.
Solution:
Given:
Resistance R = 10 $\Omega$, Voltage V = 10 V
Current I = $\frac{V}{R}$
= $\frac{10\ v}{10\ \Omega}$
= 1 A
Solution:
Given:
Resistance R = 10 $\Omega$, Voltage V = 10 V
Current I = $\frac{V}{R}$
= $\frac{10\ v}{10\ \Omega}$
= 1 A
Question 2: Calculate resistance R for the circuit
Solution:
Resistance R = $\frac{4 \times 15}{4 + 15}$ $\Omega$ + (6 + 4) $\Omega$
= 3.157$\Omega$ + 10 $\Omega$
= 13.157 $\Omega$.
Solution:
Resistance R = $\frac{4 \times 15}{4 + 15}$ $\Omega$ + (6 + 4) $\Omega$
= 3.157$\Omega$ + 10 $\Omega$
= 13.157 $\Omega$.