Tags, or attribution tags, identify the speaker of a quote.
A common problem among writers: overusing tags.
Here's an example of overusing them:
"How are you today?" asked Simon.
"I'm okay," muttered Mark.
"Just okay?" questioned Simon.
"Yeah," replied Mark.
Tags don't have to go with every phrase, especially in dialogue between two characters. Use them effectively, and your story will flow much better.
See this:
"I was thinking of you," John whispered to Elle.
"Why?"
"It just seemed like something you'd like."
Even without tags for the last two, it's clear who's speaking.
On a similar note, people often under-use beats. Most communication happens nonverbally, and you should show that in conversations.
Check out the difference between these:
Example 1:
"I'm not scared," she said.
Example 2:
She raised her chin and looked him in the eye. "I'm not scared."
One tells you what's being said; one gives you insight into the scene and the character's attitude.