Error Code P0440 - HELP ME PLEASE
 

I need some help please. My check engine light came on and my next door neighbor hooked up his car computer thing to tell me what the problem was and he said it was Error Code P0440. When we looked it up on the computer, it said it was an Evaporative Emission Control System Malfunction. Can someone tell me what this means and what part needs to be replaced?

Thanks
Jan