i have a pontiac 400 and i am trying to install a holly street avenger to the engine and there is a vacume port on the back of the old carburetor that has about five lines conected to it not includeing the other two lines so what should i do?  

First off, are you installing it on a stock intake manifold? If so you likely need an adapter plate to go from the square bore carb to the spread bore intake. Be careful of vacuum leaks around the secondaries, it will cause lots of idle and driveability problems. Having said all that, your vacuum tree accomodates different vacuum operated accesories, EGR, heat riser, cruise control, a/c etc. Compare what the old carb was hooked up to and decide what you need. Likely one of them went to the distributor for vacuum advance. Any others that you don't use can be plugged.
Steve