The possessive adjectives serve to expressive ownership or possession (hence the name). Examples in English are my, your and their. They are also called possessive adjectives because they agree in gender and number with the nouns they introduce.
Possessive articles, like all articles, must agree with the nouns they modify. Thus, if the noun is feminine, the possessive article must be feminine also; if the noun is plural, the noun must be plural as well. In the following example, the feminine noun famille requires a feminine form - sa.