Look at these examples:
Nobody said a word at the meeting. Everybody sat quietly and thought about the situation.
The boys walked quickly back to the classroom.
Quietly and quickly are adverbs. Adverbs are usually formed from an adjective + -ly (quiet – quietly, quick – quickly).
Not all words ending in –ly are adverbs. Some adjectives end in -ly as well, such as: lively, silly, lovely, elderly, friendly.
Some adverbs are irregular. This means they completely change their form such as good (adjective) – well (adverb).
Some words are both adjectives and adverbs: fast, hard, late.
The difference between adjectives and adverbs
Adjectives tell us something about a noun (something or somebody). They are usually used before the noun (a beautiful dress).
Adjectives are also used after verbs, especially to be, look, feel, sound, etc. (You are great! / She looks tired. / He is feeling exhausted.)
Adverbs tell us something about a verb (how somebody does something or how something happens).
eg. She is a serious person. (adjective)
She takes things seriously. (adverb)
Adverbs are usually used after verbs but also before adjectives and other adverbs.
My dad drives carefully.
He also drives extremely fast. (adverb + adverb)
He is extremely quiet. (adverb + adjective)