In this Lecture in the framework of the second quantizationQuantizationsecond quantization techniqueSecond quantizationsecond quantization technique we diagonalize the Hamiltonian and find the excitation spectrumSpectrumexcitation spectrum for the weakly interacting repulsive (Bogoliubov) Bose gasGasBose gas. The spectrum at small wave vectors is linear (has a soundlike character). We apply the obtained results to the search of the possible superfluidity in spin-polarized atomic hydrogenHydrogenatomic hydrogen. We analyze the condensate particle number, the correlation functions and the shift of the critical temperatureCriticalcritical temperatureTemperatureCritical temperature in the interacting Bose gasGasBose gas. We briefly consider two-dimensional case as well.