There are two vacuum hookups and one foam filter.
The vacuum hose from the fitting in the rear base of the carb goes to the single hose fitting sticking straight out the end with the wiring harness plugged into it - usually at the front. This needs to be FULL manifold vacuum.
The vacuum hose to the vacuum advance can in the distributor goes to the side-facing nipple on the 'T' fitting at the opposite end - usually the rear. The other side of that fitting - the straight out the back one - has (or had) a little square foam filter over it to filter the air going back into the hose and vacuum advance when the solenoid turns the advance off. It basically keeps the dirt out.
When the engine temp is under 85* or over 220*, the 3-prong temperature switch in the water crossover at the front of the intake activates the solenoid and allows vacuum to fully advance the vacuum advance portion of your timing.
When the engine temp is between 85* and 220*, you need to be in high gear and the switch on your manual transmission sideplate or on your auto transmission speedo cable will activate the solenoid and allow full vacuum advance.
Here's a pic with an explanation.
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