Common possessive-pronoun slips
Ten minutes on the topic's own four common mistakes: његов reached for where the subject owns the thing itself and свој is required, његов used for a female possessor instead of њен, a lowercase ваш left where a formal capital Ваш belongs, and чија forced onto a masculine noun instead of чији. Build sentences around a relative and a neighbor, catching each slip in turn, before the unit's own listening and reading put the whole topic to work.
The part of the grammar page this lesson drills — read it here, then use it.
Person-based possessives and agreement
Мој and твој decline exactly alike: мој/моја/моје and твој/твоја/твоје for masculine/feminine/neuter, моји/моје/моја and твоји/твоје/твоја in the plural. Наш and ваш follow the same pattern.
Његов (his/its), њен (her) and њихов (their) also decline like adjectives, agreeing with whatever is possessed: његов ауто, његова кућа, његово село (car/house/village) - the ending tracks the object, never the owner. Њен works the same way for a female possessor: њена кућа, њен ауто, њено писмо.
Addressing formally: ваш and Ваш
Exactly like ви/Ви in personal-pronouns-a1, ваш is capitalized Ваш when it formally addresses one respected person's possession: Ваш пасош, молим. (Your passport, please.) Lowercase ваш addresses more than one person, or one person informally.
Свој - the reflexive possessive
Use свој whenever the possessor is the same person as the subject of the clause, in any grammatical person - not only the third. Марко воли своју кућу. means Marko loves his own house; Марко воли његову кућу. would mean Marko loves some other man's house.
Свој declines exactly like мој/твој and, being reflexive, never has its own separate first- or second-person form - Ја читам своју књигу. (I'm reading my own book) is just as correct, and just as common, as using моју there.
Чији? - asking whose
Чији/чија/чије (whose) is the question word that possessive pronouns answer, and - like који/која/које in questions-a1 - it agrees with the gender and number of the thing possessed, not with whoever might own it.