In Italian possessive adjectives indicate ownership in the same way my, your, his, her, and our do in English.

Like most adjectives in Italian they also change form for the gender and plurality of the object they modify. For example, with a masculine noun “my dog” is mio cane but “my dogs” is miei cani. In the case of a feminine noun, “my cow” is mia mucca and “my cows” is mie mucche.

Suo in all its forms is equivalent to “his”, “her” and “their” in English and also “your” if you’re speaking to some formally. While “his” and “her” in English change based on the gender of the possessor, in Italian the words change based on the gender of the object being possessed.

Vostro and its related forms are used to indicate ownership when addressing a group of people informally similar to voi.
Loro has only one form is used for singular and plural objects regardless of gender.

To make any possessive adjective a pronoun you can simply add the corresponding definite article before. This changes mio (my) to il mio (mine).