Can you tell me how a chiropractor actually help correct postural distortions?

Garbage In/ Out: If the brain, much like a computer, gets poor information in, it will make decisions based upon that information. So, if joints aren't moving, and decrease information to the brain (dysafferentation), poor output to the muscles can occur. By performing chiropractic adjustments, using vibration, traction, etc. It provides input into the brain, to change the program, get better posture and function.