that
The Italian word 'quello' is used as a demonstrative pronoun and determiner like 'that' in English. It can refer to something that is not near the speaker, or to a previously mentioned situation. 'Quello' can also be used to introduce someone or something.
That is my favourite book.
In this sentence, 'quello' is used to indicate a specific item among different options, in this case, the speaker's favourite among many books.
I can't believe what I saw.
Here, 'quello' is used to refer to an event or situation, in this instance, what the speaker saw, which is hard to believe.
My dog is older than my brother's.
In this example, 'quello' is used to avoid repeating a noun (the dog) that has previously been mentioned in the sentence.