those
The Italian word 'quelli' is the plural form of 'that', and it is used to refer to multiple people or things that are not close to the speaker. Just like in English, 'quelli' should always agree in number and gender with the noun it is modifying. For example, 'Guarda quelli uccelli' means 'Look at those birds'.
Those are my friends.
In this sentence, 'quelli' is used to indicate a group of people (friends) who are at a certain distance from the speaker. It could be translated as 'those' in English.
I lost the ones I bought yesterday.
In this sentence, 'quelli' is used to refer back to something previously mentioned (the things that the speaker bought yesterday). It could be translated as 'the ones' in English.
Those are not the books I was looking for.
In this sentence, 'quelli' is used to indicate specific objects (books) that are not the ones the speaker was looking for. It could be translated as 'those' in English.