Possessives are used to indicate possession.
Usually, the order is: possessive+ substantive
Mi libro (My book).
Tu hermana (Your sister).
Su silla (His chair).
-In Spanish, singular possessives are: Mi, Tu, Su, Nuestro/Nuestra, Vuestro/Vuestra, Su
-and plural possessives are: Mis, Tus, Sus, Nuestros/Nuestras, Vuestros/Vuestras, Sus
-Possessives in Spanish are in accord with the object of the sentence.
Este es mi bolso. (This is my bag).
At times you have to combine substantive and possessive. This is the result:
-singular possessives: Mío/Mía, Tuyo/Tuya, Suyo/Suya, Nuestro/Nuestra, Vuestro/Vuestra, Suyo/Suya
-plural possessives: Míos/Mías, Tuyos/Tuyas, Suyos/Suyas, Nuestros/Nuestras, Vuestros/Vuestras, Suyos/Suyas
Here are a few examples:
Un libro mío. (A book of mine).
Una amiga tuya. (A friend of yours).
Unas cartas nuestras. (Our letters).
When speaking of parts of the human body, of clothes, or of other objects we possess, we do not use possessives.
Me duele la cabeza. (I have a headache).
Dame el jersey. (Give me the sweater).
Tengo que lavarme el pelo. (I have to wash my hair).