Will my phone use data if it's connected to Wifi?

I have an android phone with alot of apps but I don't use them that much. I have a data plan with a very small amount of data but I was told by someone if i'm connected to my Wifi that it won't use the data. Usually I do this but I just downloaded the Pandora Radio app and it warned me it would use large amounts of data and I wanted to know if i'm connected to my wifi instead if it won't use up the data? Thanks.