Mi casa es grande.
English: My house is big.
Possessive adjectives in Spanish are words used before a noun to show who owns or has something. They answer the question: Whose is it?
Use possessive adjectives in Spanish when you want to say that something belongs to someone. They go before the noun and must agree in number (singular/plural), and sometimes in gender, with the noun.
Mi casa es grande.
English: My house is big.
Tus libros están en la mesa.
English: Your books are on the table.
Su hermano vive en Madrid.
English: His/her/their/your (formal) brother lives in Madrid.
Nuestros amigos llegan mañana.
English: Our friends arrive tomorrow.
Vuestras ideas son interesantes.
English: Your (plural, informal) ideas are interesting.