In my talk I will introduce some useful elements of Kerr spacetime geometry, e.g. metric, horizons, ergosphere, geodesics, Killing vectors, constants of motion. The next step will be the process description (so called "Penrose effect" or "Penrose process"), where the particle which is coming to horizon decays to two pieces in such a way that one of them is falling down into horizon and the second one escapes to infinity with energy greater than the initial particle had. Hence, I present the maximal energy conversion efficiency for such a process and maximal energy which could be extracted in a classical way. Furthermore, this discussion will easily lead to the observation that the horizon of black hole cannot decrease (Hawking theorem) and hence, the thermodynamical description of Kerr black hole - the definition of temperature and entropy will be brought in. Finally, I will briefly introduce the "analogues" of Penrose effect for electrodynamical waves (Zel'dovich effect) and sound waves.