  This PhD thesis is divided in 6 chapters. In chapter 1 we introduce basic
superconducting phenomena. Such as, the BCS theory, the Andreev reflection and
the proximity effect, and the charge current transport in superconducting
tunnel junctions. In chapter 2 we present the Keldysh nonequilibrium Green
function formalism used to obtain the results of this thesis, together with
clarifying examples corresponding to simple junctions. In chapter 3, the subgap
transport properties of a SIF structure are studied. We devote chapter 4 to the
study of thermal transport in superconducting nanohybrid structures. In chapter
5, we develop a general theory for the microwave-irradiated high-transmittance
superconducting quantum point contact (SQPC), which consists of a thin
constriction of superconducting material in which the Andreev states can be
observed. The thesis concludes with a summary of the obtained results in
chapter 6. The detailed derivation of the quasiclassical equations is presented
in the appendix.
