This can get a little complicated. "They" does usually refer to people, but it's not so simple. "Those" can refer to a group of people or objects. When talking about animals, you can also use "they." (Those dogs in that breed are smart, and they know how to really make their owners happy).
"Those people over there, how much do you think they paid for those seats?"
"Those are the rudest people I've ever met. Do you think they try to annoy people on purpose?"
"They" is exactly like in verb tense drills: (I speak, you speak, they speak). (I know, you know, they know). But you can reference a group of something (human or not) with "those." (You see those people over there? Do you think they can tell us how to get there?")