Wanted to know exactly what this is, how it works, and how you can tell if its defective.

 

i was woundering the same thing i broke on my z6 intake manifold.

 

Its the purge solenoid.
It has to do with your emissions, sorry dont know how to test it though??

 

i don't think it will cause a problem if it was broken. it's mainly for smog check they made me put one on when I smoged my B16a

 

Gasoline releases vapors. Automakers are not allowed to just release those vapors into the atmosphere. So you have a charcoal canister that absorbs Gas vapors while the engine is off. When you turn on the engine, the ECU uses that little valve you have in your hands to send vacuum to the charcoal canister. Vacuum at the canister opens a valve that lets the accumulated gas vapors go to the throttle body where they are burnt.
That is part of the EVAP system in your car. That's why you have three hoses connected at the canister. One is for the gases from the tank, the other is for the gases to go to the throtle body and the other opens the valve that lets the vapors out. I don't know how to test it, although you could check for vacuum at the valve.
Pretty simple.