  We derive the couplings of D-branes to the RR fields from the first
principles, i.e. from the nonlinear sigma-model. We suggest a procedure to
extract poles from string amplitudes, before the eventual formula for the
couplings is obtained. Using the fact that the parts of amplitudes with poles
are irrelevant for the effective action this procedure ultimately simplify the
derivation since it allows us to omit these poles already from the very
beginning. We also use the vertex for the RR fields in the (-3/2,-1/2) ghost
picture as the useful tool for the calculation of such string amplitudes. We
carry out the calculations in all orders of brane massless excitations and
obtain the Myers-Chern-Simons action. Our goal is to present the calculations
in full technical details and specify the approximation in which one obtains
the action in question.
