I'm working on a song,I sent the vocal recording to a beat maker and he said that I sang the verse and the chorus in two different keys and that that's a problem. All I know about key is that it is a set of pitches,please help

I recommend you ask the beat maker to send back a pitch-shifted version of the verse (or chorus), adjusted so that they're in the same key! (He should be able to transpose one or the other in his editing software). That'll be the quickest solution!