Hi
You have 2 holes at each end.
Block one of the middle ones - either end will do.
From your tap - fit a pipe to one of the openings on the side, on the other side, fit a waste water pipe.
The middle which is left, this is where the purer water will come out of.
You would be better off if you put in some pre filters between the tap and ro, this will help prolong the life of it.
After the pure water comes out, you will be better off if you go through a DI resin tank, this will ensure pure water fit for window cleaning.
Hope this helps.