Possessive adjectives
A possessive says whose: my book, your house, our cat. In Spanish it sits right before the noun, and it agrees with the thing owned — never with the owner. There are five of them, one per slot of the pronoun ladder: mi, tu, su, nuestro, su. Only nuestro bothers with gender.
The five possessives
yo → mi / mis (my). tú → tu / tus (your). él, ella, usted → su / sus. nosotros → nuestro, nuestra, nuestros, nuestras (our). ustedes, ellos, ellas → su / sus. Five slots, and the bottom one is shared: the same su means 'their' and also 'your' when you are talking to a group.
It agrees with the thing, not the owner
mi, tu and su care about one thing only — how many: mi gato, mi casa, mis gatos, mis casas. The gender of the noun changes nothing; a plural noun just adds -s to the possessive. nuestro is the one that shows gender as well, because it behaves like an ordinary adjective: nuestro perro, nuestra casa, nuestros amigos, nuestras flores. Read the consequence carefully — su casa tells you nothing about who owns it, and nothing about gender either: only that there is one house.
su does a lot of work
su stands in for él, ella, usted, ellos, ellas and ustedes all at once, so su carro can be his car, her car, their car or your car. Usually the conversation has already told you which. When it hasn't, Latin America reaches for de plus the pronoun: el carro de él, la casa de ella, los lápices de ellos. And de ustedes is the everyday way to say 'yours' to a group: ¿Esta es la casa de ustedes?
Talking to a group
Plural 'you' across Latin America is ustedes — with your friends, with your family, with strangers, always ustedes. Its possessive is su / sus, the very same pair as 'their': Muchachos, ¿dónde está su casa? (Guys, where's your house?), ¿Ya tienen sus boletos? (Do you have your tickets yet?). One form for the whole group, warm or formal alike.
tu has no accent — and where the word goes
tu and tú are two different words: tu casa is your house, tú eres is you are. The accent belongs to the pronoun and only to the pronoun. As for placement, the possessive goes straight before the noun and pushes the article out: mi amigo, never el mi amigo. An adjective still follows the noun: mi amigo nuevo, nuestra casa pequeña.
