Following are situations when commas are needed:
Use commas to separate items in a series if there are three or more items. Also, use commas for a list of adjectives which independently describe a noun.
- Last weekend we did some camping, fishing, and rock climbing.
- We enjoyed the warm, sunny, beautiful afternoon.
Use a comma with a connecting word (and, but, or, nor, so, yet) when you connect two ideas in a compound sentence.
- Sam was supposed to be here, but I haven’t seen him all day.
- She told me to check at the library, so I went there this morning.
Use a comma after the first thought in a complex sentence if the sentence begins with the connecting word. Some commonly used connecting words are if, because, as, when, while, after, before, unless and although.
- Unless you call me, I will expect to meet you at noon for lunch.
- Although I dislike crowds, I enjoyed visiting New York City.