The lines should be teed together and routed to the thermostatic switch in the housing. Then, as AG said, the other line from switch to a manifold vacuum source.
As to how they operate, the system reduces the chance of carburetor icing after starting in cold temperatures. When cold, the thermostatic switch allows manifold vacuum to pass through to the doors, causing them to pull close. When closed, warm air is drawn from the exhaust manifold preheat shroud thru the "stove" pipe and into the carburetor. Meanwhile, the exhaust crossover is heating the intake plenum and warming the air charge. As the vacuum switch gradually reaches its preset temperature it slowly closes off the vacuum, allowing the spring loaded doors to open and cool, unheated air to intake.
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