What are adverbs?

We use an adverb to say how an action is performed. We call these adverbs of manner. He speaks English fluently.
She answered correctly.
We use an adverb to add information about the place or time. How long have you lived here?
Were you at home yesterday?
We can use an adverb to intensify an adjective or verb. She was extremely happy to see him again.
I really hate travelling by train.
We can use an adverb of frequency to say how often we do something. I always go jogging on Sundays.
We're vegetarians: we never eat meat.

Forms of adverbs
Most adverbs are formed by adding -ly to an adjective. nicely
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.

List of irregular adverbs
fast ⇒ fast
daily ⇒ daily
late ⇒ late
early ⇒ early
hard ⇒ hard
The adjective good is irregular: its adverb form is well. good ⇒ well
Adverbs – common mistakes
Common mistakes Correct version Why?
The camera works perfect. The camera works perfectly. We use an adverb (perfectly = adverb, perfect = adjective) when we want to say how we do something.
Did you work hardly today? Did you work hard today? Some adverbs have the same form as the adjective: hard - hard, fast - fast, late - late.
She behaved rather sillily.
She passed the exam difficultly.
She behaved in a silly way.
She passed the exam with difficulty.
Some adjectives (including many ending in -ly) don't have an adverb equivalent. Instead, we use an adverbial phrase (in a friendly manner, in a silly way, with difficulty).
His answer sounded correctly.
He looks happily.
His answer sounded correct.
He looks happy.
After linking verbs (look, sound, taste, smell, feel, seem, etc.) we use adjectives, NOT adverbs.