"O bizde yok." Translation: We do not have it.
"O" - he/she/it. Personal pronoun, non gendered.
Yok - Don't have for objects. Not a reference to a person.
"O bizde değil ." - He/She is not with us.
Yok - does not exist & (değil) - negates previous word.
Difference between (yok) - does not exist & (değil) not her/him.