The first lecture of a short course given by prof. Beretta during IAP 2008 to offer a quick view of how the general principles of thermodynamics can be very effectively presented and taught in a rigorous way, by following the treatment developed in the textbook Gyftopoulos & Beretta, Thermodynamics. Foundations and Applications, Dover, 2005. The treatment resolves conceptual loopholes and logical deficiencies which are present in traditional treatments of thermodynamics, and it is rigorous because it builds up a set of unambiguous definitions of all the basic concepts needed in the exposition. The operational definition of entropy given in this lecture is valid not only for equilibrium states but also for nonequilibrium, and not only for macroscopic systems but also for miscorscopic ones. While viewing the lecture, it may help to open a closeup of the blackboards at the end of the lecture, available at http://web.mit.edu/beretta/www/ThermoNutshellBlackboards-1.htm