The possessive pronouns in German are also known as possessive articles because they follow the four cases in German and are used as an indefinite article. In this blog post, I explain how to use possessive pronouns properly.
Unlike the personal pronouns in German wich don't have endings, the possessive pronouns do. Their endings come from the indefinite articles because possessive pronouns are actually articles in their own right. Below you see the declination of the possessive pronoun "mein" as an example.
As the table shows, the gender and case of the noun that follows determines the ending of the possessive pronoun. To learn more about gender rules in German and how to use the German cases, check out my blog entries on these topics.
Let's now look at some examples in full sentences.
Meine Nationalmannschaft hat die Weltmeisterschaft gewonnen.
(My national team won the world cup)
In this sentence, the national team is the subject and because the indefinite article would be "eine" as Mannschaft is a feminine in German, an "e" must be added to the possessive pronoun "mein"
Ich gebe meinem Bruder ein Buch
(I give a book to my brother)
Here, the brother is the indirect object (dative) as he receives the book, so your reference is the indefinite article "einer". Hence, an "er" needs to be added to "mein".
However, in nominative masculine, nominative neutral and accusative neutral, the article is "ein" without an ending. Hence the possessive pronouns don't have an ending there either.
Mein Bruder spielt gern Schach.
(My brother likes to play chess)
Mein Haus war teuer.
(My house was expensive)
To avoid a common mistake in using "sein" and "ihr", read my blog entry on the difference between the two pronouns and bear in mind that their endings are again determined by the gender and the case of the noun that follows.
Sie gibt ihrem Bruder ein Buch.
(She gives a book to her brother)
Your subject is a female and so your possessive article is "ihr". Since the brother is in the dative case, the ending "em" from the article "einem" needs to be added.
Er gibt seiner Schwester ein Buch
(He gives a book to his sister)
Here, your subject is a male, so your possessive article is "sein". As the sister is again in the dative case, the ending "er" needs to be added because the article would be "einer".
My advice would be to practice the use of articles and cases first. Once you have a good understanding of the four cases, you will find possessive pronouns much easier to use.