Reinforcers make the behavior more likely to occur again in the future.
The difference between the terms is that a reinforcer is a stimulus and reinforcment is the process of using that stimulus to change behavior. Yes, the branch of psychology that studies the biological basis of behavior and mental events is called Biological or Physiological Psychology. Somehow the brain is producing these things, and that is the great mystery which is being addressed by these researchers. Everyone who takes General Psychology should at least get a rudimentary introduction to this field. To appreciate the research findings, one must also have a general knowledge of nervous system anatomy.