Okay...so this system is pretty weird. No manual exists...
So this is how to connect this:
https/i.imgur.com/MkwKmBx.jpg
Connect this type of cable between the right and left speaker:
The middle wire (white) goes in the RED connector of the passive speaker. The black wire (or ground) goes in the black connector.
Then you connect the powered speaker to a PC, DVD, etc using the left RCA inputs. The white leftover RCA jack written OUTPUT is left unconnected.