To add to what kevbo posted above, the two most significant coding systems are ICD-9 codes and CPT codes. These systems allow for universal communication between providers and insurance companies.
ICD/International Classification of Diseases is just that…it attaches a numeric code to all medical issues/condtions
CPT/Current Procedural Terminology attaches a numeric code to designate any vists, procedures, etc.
There are certification systems for billers. If it is something you are interested in, you may want to get a job as a biller w/out being certified to see if it is worth your time/interest to get certified.