Im not familiar with BFS. So its kinda of hard to see what everything is on our picture. I have the BRS unit and its come with great instructions and was pretty much put together. I take it you bought this used? If not I would try to get some directions from BFS.
It's hard to see in 2D. Water in should be into the first filtration chamber. Then 2nd and 3rd, then into the RO membrane. Two outlets from RO cannister: one for discard water and one for RO water. Looks like maybe 2 should be water in?
Water in should go to T#6. One leg feeds the gauge, the other leg goes to #8.
#2 should go to #7
#4 is waste water.
#3 is your useable RO water.
Shut off valve should be on water in. You can also run 2 if you want but really no need. If you have a leak on the unit easier to shut off the feed than the supply.