1. Introductory Phrase: When a phrase introduces the main clause, you use a comma to separate it.
* Example: *After the long journey,* we finally arrived home.
2. Introductory Clause: If a dependent clause (one that cannot stand alone) comes before the main clause, use a comma to separate them.
* Example: *Because I was late,* I missed the beginning of the movie.
3. Introductory Word: A single word that introduces the sentence (such as however, therefore, or finally) often needs a comma after it.
* Example: *Finally,* I finished my homework.