Eli5: Why do you use “they” for non-gendered speech instead of “it”?

Question

I’m not a native speaker, but as far as I understood, for singular objects and animals “it” was used. Why use “they” for individual people then?

In: 1400

Answer 1

I have a question. If using “they” in a singular manner, referring to a single person, would it be appropriate to say:

“They is going to the store”

Or

“They are going to the store.”

I’m genuinely unsure.