This may be a dumb question but what is the difference between meu and minha? Teu and tua and teu and seu? And so on...
meu, teu, seu, nosso etc are used with masculine words. minha, tua, sua, nossa are used with feminine words.
What is the difference between minho and meu
"Minho" does not exist as a common noun (it's a name for a river in Portugal).
"Meu" is used for masculine, singular nouns. "Minha" is used for feminine, singular nouns.
Why isn't there a definitive article before the possessive?
It is opitional for possessive adjectives. Here you can use or omit it.