IMPORTANT: If you want to learn about japanese adverbs, you have to know the japanese adjectives; because most of japanese adverbs are from adjectives.
DEFINITION:
Adverbs tell us when, how, why or where the action happens. They modify a verb, a noun, an adjective, another adverb or a complete sentence. They also can provide us information about manner, quantity, frequency, time, or place.
ADVERB RULE:
You can make Japanese adverbs from adjectives in two ways:
In adjective that ends -i (い). Replacing the -i with -ku (く).
In adjective that ends -na (な). Replacing the -na with -ni (に).