Any force that involves electric or magnetic fields uses the Lorentz force equation:
$\textbf{F} = q(\textbf{E}\times\textbf{B})$
An electrostatic force comes from a static electric field, such as the one generated by a charge at rest. This force is given by $F=q\bf{E}$ since the magnetic field is zero.
Electromagnetic force comes about from the same idea, but you consider situations with accelerating charges/changing currents. This gives off radiation, which is a wave with electric and magnetic field components.
Electromotive force is from Faraday's law (in integral form): $$\oint{\textbf{E}\cdot\textbf{dr}}=-\iint_A{\frac{\partial\Phi}{\partial t}da} $$
The term on the left yields an electromotive force, which can be interpreted as the voltage around a closed loop.
Voltage difference is the difference in voltage between two points in space, where voltage represents the scalar potential of the electric field: $$\textbf{E}=-\nabla V $$