Then means at a particular time in the past or in the future.
He wanted to have a source of income after his retirement; until then, he wouldn't require additional money...
The clinic opened for business last October and since then has treated more than 200 people.
該診所去年 10 月開業，從那以后已經接診 200 多人。
Then is used when you refer to something which was true at a particular time in the past but is not true now.
...the Race Relations Act of 1976 (enacted by the then Labour Government)...
He was known by many for his role in the then record-breaking robbery of the mail train from Glasgow to London in August 1963.
他曾因參與 1963 年 8 月那起發生在從格拉斯哥開往倫敦的郵政列車上的特大搶劫案而惡名昭著。
You use then to say that one thing happens after another, or is after another on a list.
Add the oil and then the scallops to the pan, leaving a little space for the garlic...
I felt myself blush. Then I sniffed back a tear...
You use then in conversation to indicate that what you are about to say follows logically in some way from what has just been said or implied.
'I wasn't a very good scholar at school.' — 'What did you like doing best then?'...
You're not gonna tell me, are you? Do I have to guess, then?...
You use then at the end of a topic or at the end of a conversation.
'I can meet you after work. Six o'clock?'— 'Fine.' — 'Six o'clock, then?'...
“我下班后可以和你碰面。6 點可以嗎？”——“行啊。”——“那就定 6 點啦？”
He stood up. 'That's settled then.'...
(和 now，well，okay 等連用，引出新話題或新觀點)
You use then with words like 'now', 'well', and 'okay', to introduce a new topic or a new point of view.
Now then, you say you walk on the fields out the back?
Well then, I'll put the kettle on and make us some tea...
You use then to introduce a summary of what you have said or the conclusions that you are drawing from it.
This, then, was the music that appeared to dominate the world of serious concert music in the mid-1960s...
這就是 20 世紀 60 年代中期嚴肅的管弦樂中的主流音樂。
By 1931, then, France alone in Europe was a country of massive immigration.
也就是說，到 1931 年的時候，法國是歐洲唯一一個擁有大量移民的國家。
You use then to introduce the second part of a sentence which begins with 'if'. The first part of the sentence describes a possible situation, and then introduces the result of the situation.
If the answer is 'yes', then we must decide on an appropriate course of action...
畢竟，話說回來，而且(用于句首，或用于 and，but 之后引出對之前所說話的評論或補充)
You use then at the beginning of a sentence or after 'and' or 'but' to introduce a comment or an extra piece of information to what you have already said.
We have to do quite a bit of reading, and then we have our ongoing work which would be an essay...
He sounded sincere, but then, he always did.