In chapter 6 we set the problem of calculating the correlation functions in quantum field theory. The subsequent chapters were devoted to the solution of this problem in the framework of the loop expansion. What is the parameter of this expansion? Why is it so called? How restricted is its domain of applicability? Is the <p4-model really the simplest field theoretic one? In this chapter we try to answer these questions, but first we would like to calculate the correlators of the type (6.5) - (6.7). We shall express them through the effective action (introduced in chapter 6) which contains complete information about all the Green's functions of the theory in the most compact form.