What exactly does a medical biller/coder do?

I'm thinking of going back to school to go into the medical field because I know those are the jobs that are probably the most secure in this tough economy. I know that I'm not a really compassionate person so I know I wouldn't be very good with patients so I was wondering if a medical biller/coder is a job that would probably be for me. How much do they make? How long do you have to go to school for this? Thanks for your help.