” You can use “therefore” in the middle of a sentence that includes 2 independent clauses, but not a sentence that contains dependent clauses. An independent clause can stand alone as a sentence, or you can separate independent clauses using a semicolon.  For example, “therefore” can be used to separate 2 clauses like, “California is a coastal state. It has many beaches.” You would rewrite it to say, “California is a coastal state; therefore, it has many beaches.” In some cases, you can also use “therefore” to start a sentence. For example, “June’s car broke down on her way to work. Therefore, she was late for the meeting.” Remember that “therefore” needs to be ‘’between’’ 2 independent clauses, not after them. “Therefore” is not a word that should be used too often in writing. It will sound best if you use it sparingly, so take care not to overuse it. Use other transition words to vary your sentences, such as “so,” “then,” “accordingly,” “consequently,” “thus,” or “since.”  For instance, you could replace “therefore” with “thus” in the previous example. You would say, "California is a coastal state; thus, it has many beaches." Remember to always make sure that the alternative word or phrase you use will work the same way as “therefore” for the sentence. If you aren’t sure, look it up on a site like https://owl.english.purdue.edu/owl/owlprint/574/. “Therefore” is not used as often in speech as it is in writing because it can sound a bit too formal for everyday conversations. For this reason, you may want to avoid using “therefore” when you are speaking in most cases and opt for more casual transitions, such as “so” and “then.”  For example, it might sound a little odd to people if you said, “It was raining when I left for work this morning, therefore I needed my raincoat.” An exception to this rule might be if you are giving a speech or presentation.

TL;DR in Chinese:
使用“therefore”分隔独立的从句。 谨慎使用“therefore”。 尽量在书面语而不是在口头语中使用“therefore”。