Abstract: Scientists and engineers use several techniques in solving continuum or field problems. Loosely speaking, these techniques can be classified as experimental, analytical or numerical. Experiments are expensive, time consuming, sometimes hazardous and usually do not allow much flexibility in parameter variation. However, every numerical method, as we shall see, involves an analytic simplification to the point where it is easy to apply the numerical method. In spite of this fact, the following methods are among the most commonly used in Electro Magnetism (EM). In general these methods could be divided in: Analytical Methods and Numerical Methods. Application of these methods is not limited to EM-related problems; they find applications in other continuum problems such as in fluid, heat transfer and acoustics. In this study, the FDM has been elaborated. In the beginning approximate methods in general have been elaborated. The finite difference techniques are based upon approximations which permit replacing differential equations by finite difference equations. These finite difference approximations are algebraic in form; they relate the value of the dependent variable at a point in the solution region to the values at some neighboring points. From the results we can see that for case when we have uniform distribution of the electric charges inside the cube, we obtain maximum of the potential in the center of cube, whereas if we have inside the cube only one electric charge we will obtain so-called Green function. From the results we can see that the accuracy increases with increasing the number of grid points and iterations.