Another dumb chain ?
 

I just got a chain for my bike and then onld one i took off is a few links shorter then the one i just got. Is it a must to get it shortend to the langht of the old and original chain or can i leave it alone and be just fine.

If your chain is too long, you won't be able to ride in the small chainring and smaller cogs due to the extra slack that can't be taken up by the dérailleur. It would be best to have the shop cut the chain for you...or get a chain tool to do it yourself.

How much dose that cost?

A chain breaker is cheap and a good thing to have around: $9.99 Performance Bike, http://www.performancebike.com/bikes..._1030368_-1___.

Hopefully you bought the chain at your local bike shop. Don't be afraid to ask these kind of questions to them next time.