Dummy pronouns function grammatically the same as other pronouns, except they do not refer to a person or thing like normal pronouns do.
Theirs vs. There's
"Theirs" and "There's" have pretty similar pronunciations, but have different meanings and functions. To learn about their difference, read this part.
'It' is a third-person singular pronoun. Here, we will take a close look at its functions and grammatical rules in the English language.