This video is an explanation for the question "What's the difference between 'bom' and 'boa'?" As a quick answer, I would say that "bom" is an adjective that should be used whenever you want to say that a masculine "thing" or "person" is good (since everything in Portuguese has gender). "Boa" is its equivalent for the feminine. Both mean good, but since in Portuguese adjectives should agree with the gender of their nouns we have "bom" for masculine and "boa" for feminine.