The critical behavior of a 3D Ising-like system is studied at the microscopic level of consideration. The free energy
of ordering is calculated analytically as an explicit function of temperature, an external field and the initial
parameters of the model. Within a unified approach, both Gibbs and Helmholtz free energies are obtained and
the dependencies of them on the external field and the order parameter, respectively, are presented graphically.
The regions of stability, metastability, and unstability are established on the order parameter–temperature
plane. The way of implementation of the well-known Maxwell construction is proposed at microscopic level