Don,they are two different voices.

Chest voice is low,powerful and heavy.It comes frome the chest. Head voice is higher,thinner and light.Comes from throat and nose.

There's also the middle register which I guess (correct me if I'm wrong since my formal schooling in this is very little)is my main problem. I also never understood if women have falsetto or they don't.I often read that there are 3 register for men (chest,head and falsetto) and just 2 for women (chest and head),is it right?