  Here presented a systematic study of
superconductor-constriction-superconductor contacts realized by a
break-junction technique in layered superconductors. Depending on the
constriction transparency the tunneling and SnS-Andreev spectroscopies could be
used, for the direct determination of values of superconducting gaps,
characteristic BCS-ratios and gap temperature dependences in cuprate
superconductors, magnesium diboride, novel pnictides and chalcogenides. Basing
on these data, one can estimate the gap anisotropy magnitude as well as values
of electron-boson coupling constants. We discuss the advantages and
difficulties of the break-junction technique and demonstrate this method is
powerful enough for high-resolution investigation of optical phonon modes in
high-temperature superconducting cuprates and for creating of the contacts with
the selective transparence in Mg$_{1-x}$Al$_x$B$_2$ compounds.
