Good job! Commas are indeed used to set off nonessential phrases. Nonessential phrases are additional information in a sentence that can be removed without changing the meaning or structure of the sentence. These phrases provide extra details or descriptions but are not crucial to understanding the main point of the sentence. When using commas to set off nonessential phrases, you can easily test if the information is necessary by temporarily removing the phrase from the sentence. If the sentence still makes sense without it, then it is nonessential and should be separated by commas.
