What are adverbs?

We use an adverb to say how an action is performed.

He speaks English fluently.
She answered correctly.

We use an adverb to add information about the time/place/manner.

How long have you lived here?

We can use an adverb to add information to an adjective.

She was extremely happy to see him again.
I really hate travelling by train.

Most adverbs are formed by adding ly to an adjective.
There are some exceptions - irregular adverbs.

nicely, quickly, beautifully, happily, economically

If the adjective ends in ic we add ally.

basic - basically, dramatic - dramatically

Some adverbs are irregular: they have the same form as the adjective.

The adjective good is irregular: its adverb form is well.

fast, daily, late, early, hard

good - well

The camera works perfectly.

We use an adverb
(perfectly - adverb, perfect - adjective) when we want to say how we do something.

Did you work hard today?

Some adverbs have the same form as the adjective: hard - hard, fast - fast, late - late.

She behaved rather silly.

Adjectives ending in -ly have the same spelling in the adverb form (friendly - friendly, early - early, likely - likely, lonely - lonely, ugly - ugly, silly - silly).

His answer sounded correct.
He looks happy.

After 'linking' verbs (look, sound, taste, smell, feel, seem) we use adjectives not adverbs.