They’re is short for they are. They are going to the cinema tonight. / They’re going to the cinema tonight.
Their shows possession. It means it belongs to them. They wanted to give me their books.
There refers to a place. I’m going to sit over there now.
Keywords = today, at the moment, now
I am working in the office today. I am not working at the moment. Wir benutzen die -ing Form für vorübergehende Situationen.