their
The Italian word 'loro' is used to indicate possession for multiple persons. Similar to 'their' in English, it is used before the noun that is being possessed. For example, 'Il loro libro' would translate to 'Their book'.
They are reading a book.
In this sentence, 'Loro' is used as a subject pronoun that means 'they'. The verb 'leggono' is used in the present tense to indicate the action 'they' are doing at the moment, which is reading ('leggono' means 'they read'). 'Un libro' means 'a book' in English.
The dog is theirs.
In this sentence, 'Loro' is used as a possessive pronoun that means 'theirs'. So, 'Il cane è il loro' literally translates to 'The dog is theirs.' 'The dog' is 'Il cane' in English and 'is' is 'è' in Italian.
They sing a song.
In this sentence, 'Loro' is used as a subject pronoun meaning 'they'. 'Cantano' is the present tense form of the verb 'cantare', which means 'to sing'. 'Una canzone' translates to 'a song' in English. Thus, the whole sentence translates to 'They sing a song'.