As part of powering the engine, you need some cold gas and hot gas. This room, found west of the engine proper - itself found in the northern part of the station, inner side - concerns itself with the latter, by running gas under the heating chamber and/or directing it towards the furnaces, all in the engine room proper.
Wrench gas canisters down and open the relevant valves. The upper pair feeds into the hot loop, while the lower pair feed into the combustion chamber; you'll also need to use the Pump Control Room to let the lower ones actually feed into the chamber. The middle one leads directly into space, which you usually probably don't want to do.
There is no vent. You might want to make your own sort-of vents by RCDing the floor apart, though, I think.
The APC for this room is on the west wall. The lower one you see in the screenshot is for the Engineering Gas Storage room.