Two point charges exert forces on one another along the line joining them. Coulomb's law gives the magnitude of that electrostatic force:

$$F=k\frac{|q_1q_2|}{r^2},$$

where $r$ is the separation and

$$k=\frac1{4\pi\varepsilon_0}.$$

Direction

Like charges repel and opposite charges attract. The force on one charge is equal and opposite to the force on the other, in agreement with Newton's third law.

Inverse-square behavior

Doubling the separation reduces the force by a factor of four. Doubling one charge doubles the force.

Superposition

With several source charges, the total force on a chosen charge is the vector sum of the individual Coulomb forces:

$$\mathbf F_{\mathrm{net}}=\sum_i\mathbf F_i.$$

Coulomb's law describes point charges directly. The electric-field concept separates the influence of the source charges from the particular test charge placed in that influence.