What’s the deal with military MOS, AFSC and Rates?

Unless you have a military background or have been involved with hiring large numbers of military people, figuring out military skills is a daunting task.  The Army and Marine Corps use “MOS” groups (Military Occupational Specialty).  The Air Force separates their skills into “AFSC” groups (Air Force Specialty Codes).  Finally, the Navy calls each of [...]