This is the 68th most frequent Azerbaijani word.
onlar
"They" or "them" in English.
In this sentence, 'Onlar' serves as the subject pronoun referring to multiple people performing the action of going.
Onlar məktəbə gedirlər.
They are going to school.
Here, 'onları' is the accusative case form of 'Onlar', used to indicate the direct object of the verb 'gördüm' (I saw).
Mən onları parkda gördüm.
I saw them in the park.
In this sentence, 'onların' is the possessive form of 'Onlar', indicating that the books belong to the individuals denoted by 'Onlar'.