Possession: 's, of, my / mine

• 's for people and animals: Anna's car, my brother's wife, the dog's bed.
• Plural ending in -s → only the apostrophe: my parents' house (two parents). Irregular plural → 's: the children's room.
• of for things and parts: the end of the film, the roof of the house. Time expressions take 's: today's newspaper, two weeks' holiday.
• 's can stand alone for shops and homes: at the doctor's, at Mark's (at Mark's place).

Traps: its (possessive) has no apostrophe — it's = it is / it has. their (possessive) ≠ there (place) ≠ they're (they are). “A friend of mine” = one of my friends. Whose is this? = Who does it belong to?