Adjectives ( careful/quick) tell us something about the noun (somebody or something) . We use adjectives before nouns .
John is a careful driver .
They didn’t come because of the heavy storm .
I was admiring the beautiful flowers.
Adverbs (quikly/carefully etc ) tell us about a verb ( how somebody does something or how something happens)
Alice drove carefully along the narrow street.
My brother didn’t go out because it was snowing heavily.
The cat was walking silently .
PLEASE COMPARE !
She speaks perfect English . -Here ‘perfect’ is an adjective because it describes the noun ‘English’.
She speaks English perfectly . Here ‘perfectly’ is an adverb because it describes the verb ‘speak’.