What brand / model do you have? How many clear round canisters? Can you post a pic of the unit? You should be able to find a manual online, even if it's not the exact unit you have they all work pretty much the same.
The short of it is you will have;
-a line for tap water in
-a line for waste water out
-a line for product water out.
Depending on the unit, you may also have one or two bypass/flush valves and lines, a pressure gauge, auto shut off unit, and or inline TDS meter. (a pic will tell a thousand words here)