"Ele explica o seu livro."

[samosborn88]

why is it not "o livro dele"?
Can anyone explain the differences of when to use seu/sua or dele/dela/deles/delas for possession?

[Paulenrique]

You can use dele. His = seu/sua/dele. Her = seu/sua/dela. Your = seu/sua. Their = seus/suas/deles/delas. When we want to defferenciate seu/sua to 2nd and 3rd persons, we use dele/dela. Sometimes it can be tricky. Use dele/dela always after the possession. His car = seu carro/ carro dele. Seu/sua goes according the gender of the adjective and number. His car = seu carro/carro dele his house = sua casa/casa dele, his cars = seus carros/carros dele, his houses = suas casas/casas dela