  N=2 supersymmetric Yang-Mills theories for all classical gauge groups, that
is, for SU(N), SO(N), and Sp(N) is considered. The formal expression for almost
all models accepted by the asymptotic freedom are obtained. The equations which
define the Seiberg-Witten curve are proposed. In some cases they are solved. It
is shown that for all considered the 1-instanton corrections which follows from
these equations agree with the direct computations. Also they agree with the
computations based on Seiberg-Witten curves which come from the M-theory
consideration. It is shown that for a large class of models the M-theory
predictions matches with the direct compuatations. It is done for all
considered models at the 1-instanton level. For some models it is shown at the
level of the Seiberg-Witten curves.
