The Polish genitive indicating possession

Possession in English is shown using the apostrophy 'my grandfather's' wife' or 'my sister's house', and very confusing it is to.

Who really knows where to put the apostrophy?

Polish uses the genitive case to do the same thing. Another way to write 'my grandfather's' wife' is 'the wife of my grandfather' and this is how it is done in the Polish language.

The Polish word for grandfather is dziadek in the dictionary or nominative form, and dziadka in the genitive. Dziadka has the meaning 'of grandfather' and so we have żona dziadka for 'my grandfather's wife'.

żona pana Nowaka Mr Novak's wife (the wife of Mr Novak)
dom matki mother's house (the house of mother)
żona dziadka grandfather's wife (the wife of grandfather)
Błędy uczniów errors of students

See, forming the genitive, for an a broad brush approach to forming the genitive of nouns.