If you buy the kit it should have instructions. Basically, the line from the Carbon Filer to the RO
Membrane goes through one set of ports on the solenoid and the discharge line goes through the check valve first then through the other ports on the solenoid and on to the float valve. When the float valve closes, it builds up pressure which causes the solenoid to close stopping water from going to the RO
Membrane (and consequently out the waste line). The check valve makes sure that the pressure doesn't bleed off. As soon as the float opens again, pressure will bleed off allowing water to flow.