it's really just an exclamation of excitement. it comes from a character called ernest p worrell, who was kind of a caricature of an unintelligent back woods type person from a state like kentucky. he uses his golly bob howdy catch-phrase to show excitement

Golly means wow, a surprise😯 Bob is just a name really Howdy is a way to say hi, usually used by Cowboys Put together it’s just a silly way to say wow It would not be used commonly