This is the 190th most frequent Polish word.
naszej
"Naszej" means "our" (feminine singular, genitive or locative case) in English.
The word 'naszej' is used here to denote possession ('our') in the genitive case, referring to 'mom' ('mamy').
To jest samochód naszej mamy.
This is our mother's car.
In this sentence, 'naszej' indicates possession ('our') and is used in the genitive case to describe 'school' ('szkoły').
Podoba mi się ogród naszej szkoły.
I like the garden of our school.
Here, 'naszą' refers to possession ('our') and is used in the instrumental case to modify 'village' ('wioską').