What is a Comma?
You know, that squiggle that goes on the bottom of the line. Just what is it good for? You might think a comma is solely for slowing things down, but that's not at all true.
A comma has many different uses. I'll go over a few of them here. One, it's used to separate independent clauses (i.e., statements within a sentence that can stand on their own). By using them, you can avoid run-on sentences. Take the following classic sentence: "I came here to chew bubblegum and kick ass, and I'm all out of gum." Both "I came here to chew bubblegum and kick ass" and "I'm all out of gum" are independent clauses. Often, independent clauses are separated by coordinating conjunctions such as "and," but that's not always the case. Note that there is no comma after the first "and" because "kick ass" is not an independent clause, meaning it can't be it's own sentence.
You also use them after a "Yes" or "No" that begins a sentence. As in, "Yes, I came here to chew bubblegum and kick ass." Ditto for introductory adverbs. In the sentence, "Finally, I came here to chew bubblegum and kick ass," you have a comma after "Finally."
Say, did you notice how I used a comma to introduce quotations in that last paragraph? Yep, you use commas that way as well.
Finally, let's talk about numbers. You use commas to denote numbers larger than three digits. Let's take 1983, the year in which I was born. As a year, you wouldn't put a comma in it. But as a number, you would make it 1,983.
That's all for now. There are even more rules for comma usage that you can find at https://www.businessinsider.com/a-guide-to-proper-comma-use-2013-9.