Although neutrinos are the second most abundant particles in the universe after photons, they are among the least well understood subatomic particles. The experimental evidence of phase transitions (neutrino oscillations) between neutrino flavors showed that neutrinos cannot be massless as predicted by the Standard Model, and this led to increasing the interest in experimental neutrino studies. Since neutrinos feel only the weak interaction, they continue on their way without much interaction with matter and carry serious information about their sources. Since neutrinos emerge 24/7 from different sources: from nuclear reactions in the sun and stars to supernova explosions, from radioactive formations on the earth to reactions in nuclear reactors, this shows that they are very important particles, which need to be fully understood.