Fetching details from the dictionary...
that; it
then; that point (in time); that time
それは昨日買った本です。
That is a book I bought yesterday.
それを聞いて少し安心しました。
I felt a bit relieved to hear that.
それがいつ届くか分からないので、毎日確認している。
I don't know when it will arrive, so I check every day.