Question

How did the gods and goddesses become gods and goddesses

Answer 1

(I'll just use Greek mythology as an example)
The god and goddesses within the Greek mythology were birthed from many pieces of fictional literature at the time published by poets and philosophers at the time like Homer. The divine beings often represented the powerful forces of nature and human nature, to put in perspective at the insignificance of mortals below. 
That's my take on it, more context for future questions would be appreciated, cheers.