meu is male (meu carro) minha is female (minha casa) meus and minhas is plural (os meus carros / as minhas casas)
Meu = First person possessive pronoun for singular masculine nouns e.g. Eu amo meu cachorro (I love my dog)
Meus = First person possessive pronoun for plural masculine nouns e.g. Eu ficarei com meus amigos (I will stay with my friends)
Minha = First person possessive pronoun for singular feminine nouns e.g. Eu viajarei com minha namorada (I will travel with my girlfriend)
Minhas = First person possessive pronoun for plural feminine nouns e.g. Eu cuido bem das minhas flores (I take good care of my flowers)
The only reason i say Frank's answer is more "better" is because he explained it in simple terms. Many new beginners, even myself dont understand "first person possessive pronoun" it's a mouthful!
Thanks for the advice!
I agree with you that is extremally detailed, but I personally like this kind of answers because it can help in the future. And it can help others that may see this discussion. Since there was a simpler explanation, I took the liberty of giving one long and boring (and this is the kind of answer you get in highschool if you ask a portuguese teacher. Portuguese is a language with long and boring grammatical rules).
MEU= Exemplo: Meu carro, meu celular, meu tablet..
MEUS= Exemplo: Meus cachorros, meus gatos, meus doces.. (no plural)
MINHA= Exemplo: Minha mae, minha irma, minha amiga...
Espero ter te ajudado! Bjs e bons estudos!