An adverb is a descriptor such as: She rubbed her eyes and said tiredly, “These adverbs are so redundant.”
Consider that sentence. The word “tiredly” didn’t need to be there, because we already indicated she was tired by saying she “rubbed her eyes”. Recognisable by their ‘ly’ ending, adverbs are scattered through the copy, but they tend to appear around dialogue most of all. So why is it so bad add an adverb? Because you are committing the sin of “telling” (tiredly) instead of “showing” (rubbed eyes) the reader what is happening, and when you do that, the reader disengages.
Overuse of adverbs is one of the first signs an editor or publisher looks for to gauge the experience level of a writer.
There are exceptions to this rule, such as when the adverb is contradictory, such as: Smiling sweetly she said, “I can’t stand your face.” Without the adverb, we wouldn’t have known the full extent of her sarcasm, as a sweet smile is different to a dry, brittle or cold one.
As Stephen King says,
Use Adverbs like they’re hundred dollar bills.
Likewise, don’t feel that you need to stipulate that ‘he said’ or ‘she answered’ every line of dialogue in your story. Unless it isn’t clear who is saying a line at any given time (for this reason it’s advisable to limit the characters speaking in a scene to three, where possible) there’s absolutely no need to include it. Remember, every single word has to work for it’s right to be in your writing, even the ‘he said, she saids’.