  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.
