Status and Updated Results of the OPERA Experimental Search for $ \nu_{\mu} \to \nu_\tau$ Oscillations.

The OPERA detector in the underground Gran Sasso Laboratory (LNGS) has been designed to detect muon-neutrino to tau-neutrino oscillations in direct appearance mode. The hybrid apparatus consists of an emulsion/lead target and of electronic detectors. Data taking using the CNGS muon-neutrino beam from CERN took place from 2008 to 2012. The various steps of the analysis are described, from the localization of the target element where a neutrino interaction occurred up to the identification in the emulsion films of the decay vertex of a short lived particle. The detailed simulation of the different steps allows a precise evaluation of the signal efficiency and of the associated backgrounds. The significance of the latest tau-neutrino appearance results is discussed.