Complex sentence: The residual salty liquid from that first stage is introduced into a second flash evaporation stage at a pressure lower than the first stage pressure where more water is flashed into steam which is also subsequently condensed into more salt-free water.
Split into simpler sentences: The residual salty liquid from that first stage is introduced into a second flash evaporation stage at a pressure lower than the first stage pressure. More water is flashed into steam which is also subsequently condensed into more salt-free water.