A soft EVAP hose connects to there, then if you are standing at the front of the car, look left and there is a wiring harness, it should have wires for the injectors, and what not coming out of it, there should be a hard plastic T in it that goes inside the car around the passenger door area, that provides vacuum for the HVAC to switch from vent, to defrost, to floor.
The other part of that T runs inside the wiring harness till it gets near the front of the car near the battery area, then it comes out and runs underneath the bumper area, then it makes its way to the EVAP canister which is under the airbox/PCM..
I can try to get some pics for you ASAP if needed, I had to replace all of those soft EVAP hoses and connectors not too long ago, they were all dry-rotted.
2006 Pontiac Grand Prix GT with SC
1996 Buick Park Ave NA