Commas help determine the meaning of a sentence. Sentences that lack commas where they are necessary can be very difficult to decipher. Sentences that include commas where they should not be are also confusing and can even make the author look foolish.
Here are two resources to help you understand how to properly use commas:
1. "17 rules for using commas correctly without looking like a fool" by Business Insider. Note: This article refers to "dependent" and "independent" clauses. For more information on those, click here.
2. Commas (Eight Basic Uses) - this is a downloadable worksheet.