It's a Nova quad processor, the last slot can be set up as a washing slot, using the small spigot for incoming water, and the larger one at the back for the outflow. I have mine set up for two-bath fixing, that is, I have fixer in the last two slots, then pull the fixed print out and into a separate holding tray.
As I recall, these were originally sold for color work, so the final wash would be short. For B&W, and especially fiber papers, using the last slot for washing isn't very practical, so I use it for the second fix bath. If you don't use 2 bath fix, just put water there, but you'd probably want to wash prints in a separate washer or tray.
The two holes on top are for filling the water bath, on the side under them should be two rubber plugs, you fill the water bath until the water gets to the level of those holes then insert the plugs. Do not operate the heater without water in the bath.
Your unit (like mine) has Nova's older style heater. They have an upgrade kit with a different style heater that has just one green block, as I recall. I leave mine near the minimum heat setting to maintain 68F/20C which is nice in the winter when the room temperatures are a bit lower than that.
Nova's web site has replacements for the spigot tubes, valves and the short rubber hoses. The glued-in tubes that are under the rubber become brittle after a while from the chemistry and need to be drilled out and replaced. I've had to do do this with two of mine so far. Just be careful to not stress the tubes if you move the unit around.
The also have an outlet kit for the large outlet in the last slot if you want to use it for a wash.
Your pictures don't show them, but it should have come with clips that hold the paper in the slots. If it didn't you'll need to buy some from Nova, or else cobble up substitutes. It would be difficult to work with without them. The clips are available on Nova's website.
I really like mine, and it saves a ton of room over 4 equivalently sized trays. I keep mine plugged in an on all the time, so to start a printing session I just remove the floating lids and turn off the lights. Most developers will last a good while in in the slots. Depending on how much printing I do, I've gone as much as three weeks between developer change-outs.