As promised, here's another blog post about punctuation. We don't have room here for me to go into every single rule, but here are a few to get you started.
First off, let's talk about direct address in dialogue. That's when your character is talking to another character and he calls her by name.
"Hey, Sally!" Bill called.
Notice that because he's talking directly to her, we put a comma before her name.
If he's talking about Sally, there's no comma.
"I wonder where Sally went," Bill said.
Now let's talk about punctuation to attach a speech tag to a speech. A speech tag, dialogue tag, or just plain tag is what tells the reader who is speaking. For instance:
You attach a speech tag to the speech with a comma. Like so.
"I'm sure glad you came over tonight," Bill said.
I've seen some authors use a period after "tonight," and that's incorrect.
You use a period when you're using a beat. What's a beat? An action that shows who's talking. Like so.
"I'm sure glad you came over tonight." Bill uncorked the sparkling cider and poured her a glass.
Notice the period in there. Don't get confused and use a comma.
Here's a little trick to remember the difference.
A comma is shaped like a tag. So you use a comma with a tag.
Have fun, and happy writing!