Complex sentence: Neutrinos are produced in a way that conserves lepton number; i.e., for every electron neutrino produced, a positron (anti-electron) is produced, and for every electron antineutrino produced, an electron is produced as well.
Split into simpler sentences: Neutrinos are produced in a way that conserves lepton number. So for every electron neutrino produced, a positron (anti-electron) is produced, and for every electron antineutrino produced, an electron is produced as well.