They are plural forms of the accusative pronoun it. Jim, you can't put your shoes here. Put them away.
They are the plural forms of the third person, regardless of gender, representing some people or things that have been mentioned, and are often used as subjects in sentences, usually after the nouns it refers to.
Its usage:
1, used as a personal pronoun, can replace inanimate objects or things, and can also refer to people with ominous or indifferent gender, especially when they are babies.
When the subject, it can refer to weather phenomena, seasons, time, distance, natural environment and so on.
3. it can be used as a antecedent, emphasizing the subject, object, adverbial of time, adverbial of place, prepositional object or clause in sentence patterns, and emphasizing that it in sentence patterns generally refers to what has happened, not what has not happened or what has been talked about.
4. It is also often used as a modal subject or modal object, rather than a long real subject or real object (its modality is common in adjective infinitive phrases or that clauses, etc. ).
5. It can replace a proper noun, pronoun or sentence mentioned above, but it is often omitted after words such as believe, expect, forget, imagine, remember and think.