Electric Potential:
When a testcharged particle is brought from infinity to a point in the electric field then the work done per unit test charge particle is called
electric potential. It is represented by $V$. It is a scalar quantity.
Let's consider a testcharged particle $q_{0}$ bring from infinity to at a point $P$ in the electric field. If the work done by test charged particle is $W$ then electric potential →
Unit of Electric Potential: $Joul/Coulomb$ OR $Nm/Amperesec$
In MKS: $Kgm^{2}Ampere^{1}sec^{3}$
Dimension of Electric potential: $[ML^{2}A^{1}T^{3}]$
The electric potential at a point due to point charged particle:
Let us consider, a source point charge $+q$ is placed in air and vacuum at point $O$.Let's take a point $P$ at distance $r$ from the source point charged particle. Here the testcharged particle $+q_{0}$ is brought from infinity to point $P$.If the testcharged particle moves a very small distance $dx$ from point $A$ to $B$ against the electrostatic force. So electrostatic force at point $A$ which is placed at a distance $x$ from point $O$ →
$F=\frac{1}{4\pi\epsilon{0}} \frac{qq_{0}}{x^{2}} \qquad(1)$

Electric potential due to point charge 
The work is done against the electrostatic force $\overrightarrow{F}$ to move small distance $dx$ from point $A$ to Point $B$
$ dW=F\: dx$
$ dW=\frac{1}{4\pi\epsilon{0}} \frac{qq_{0}}{x^{2}}\:dx$   (from equation $(1)$ )
The total work is done in moving the charge $q_{0}$ from infinity to the point $P$ will be
$W=\int_{0}^{W}{dW}$
Here negative sign shows that the work done from infinity to at point $P$ is stored in the form of potential energy between the charges.
$ W=\int_{\infty}^{r}{\frac{1}{4\pi\epsilon{0}} \frac{qq_{0}}{x^{2}}\:dx }$
$ W=\frac{qq_{0}}{4\pi\epsilon{0}} \int_{\infty}^{r}{\frac{dx}{x^{2}} }$
$W=\frac{qq_{0}}{4\pi\epsilon{0}} \left [\frac{1}{x} \right ]_{\infty}^{r}$
$ W=\frac{qq_{0}}{4\pi\epsilon{0}} \left [\frac{1}{r}\frac{1}{\infty} \right ]$
$W=\frac{qq_{0}}{4\pi\epsilon{0}} \left [\frac{1}{r} \right ]$
$ W=\frac{1}{4\pi\epsilon{0}} \left [\frac{qq_{0}}{r} \right ]$
Hence, the work is done to move a unit test charge from infinity to the point $P$, or the electric potential at point $P$ is →
$V=\frac{W}{q_{0}}$
$V=\frac{1}{4\pi\epsilon{0}} \frac{q}{r}$
