I would say "How to Use Commas" but that will raise too much debate. Believe me: I've seen a group of English teaching assistants argue about commas for more than an hour. Ugly.
What I do want to convey is the ease with which a writer can learn to love (and use) commas well.
So let's start here (can you read this):
Would you read it in your head? Of course not. Music is intended for the ear. So are words. Reading silently ("in our heads") is a recent invention. Once upon a time, few could read. Books were expensive, difficult to reproduce, and precious things. (Ah, but now we have e-books and POD.) Punctuation symbols, like the comma, were invented to convey a message to the reader. Think of the comma as a rest, just like the rest in music. Where that rest is placed changes the meaning of a phrase, just like a well-placed pause in music can change the dynamic or rhythm of a song.
Take this well-circulated phrase to understand the importance of punctuation (and commas):
Woman without her man is nothing
Notice I didn't punctuate the sentence. How would you do it?
Woman: without her, man is nothing.
Woman, without her man, is nothing.
Wow. Big difference, right? We all know the famous "eats shoots and leaves" example.
So how does a writer learn to love commas? I suggest you must, must read your work aloud. I've done so with every story, book, and essay I've written in the last ten years. Commas were invented in an era of reading aloud. Meaning is conveyed through the way they make a sentence sound. You'll notice improper comma use much better through your ear.
For a more "academic" look at the comma, please visit Purdue University's Online Writing Lab (OWL).