Flow of electric current occurs only in the presence of potential difference and it flows from higher potential to lower potential. This is similar to:

• Heat Transfer: It flows from body at higher temperature to a body at lower temperature.
• Water flow: It flows from high pressure to low pressure.
• Free fall: A body falls from point of higher gravitational potential to a point of lower gravitational potential. 

Rate of flow of charge through a given cross-section of a wire is called electric current. 
It is given by the formula, $I=\frac{Q}{t}$

The electric potential difference between two points in an electric circuit is the work done in moving a unit positive charge from one point to the other.
Potential difference, $V=\frac{Workdone}{Charge}=\frac{W}{Q}$

According to Ohm's Law, the current flowing in a conductor is directly proportional to the potential difference across its ends provided the physical conditions and temperature of conductor remains constant.
$I\propto V$
$V=IR$

Resistance($R$) of a material is a measure of the obstruction offered to the flow of current through the material. It is caused due to inter-collisions of electrons. It is a function of the material, dimensions and the temperature of the resistor. For conductors, resistance increases linearly with temperature. It unit is $1\Omega (ohm)=1{VA}^{-1}$.
$R=\frac{\rho l}{A}$
where,
$\rho :$ Resistivity, function of the nature of material 
$l:$ Length of the resistor
$A:$ Area of the resistor 

For resistors $R_1,R_2,....R_n$ in series:
$R_{eq}=R_1+R_2+....+R_n$
$I_{eq}=I_1=I_2=....=I_n=I$
$V_{eq}=V_1+V_2+....V_n$

For $n$ resistors in parallel:
$V_{eq}=V_1=V_2=....=V_n$
$I_{eq}=I_1+I_2+....+I_n$ 
$\frac{1}{R_{eq}}=\frac{1}{R_1}+\frac{1}{R_2}+....+\frac{1}{R_n}$

According to Joule's Law of heating, heat generated in a conductor is given by:
$H=VIt=\frac{V^2}{R}t=I^{2}Rt$

Electrical power is given by: $P=H/t=VI=I^{2}R$
Its unit is $W$ (Watt).