RO Filter questions

[Slyguy00]

So I just got an ro filter system, and have my plumber friend hooking it up. But he seems to think its hooked up incorectly and the instructions included are beyond garbage. How do I know if everything is hooked up right, and im actually getting RO water coming out. Is there a way to test or prove the water is ro? The shutoff valve that has 4 hoses connected to it, doesnt seem to make sense. Any information I can find online doesnt seem to help. Its a crystal clear 100gpd ro filter system. And info would be a huge help. Thanks