An adverb describe the manner and nature of an action. It's a mix of adjective and verb, serving the purpose of both, usually based on verbs, but in some cases nouns, depending on expression.
In many cases an adverb is a descriptor of 'how' an action or subject is defined.
Sentence structures vary. The structure must refer directly to the subject, however constructed:He acted quickly.
Quickly he acted.
Acting quickly, he...
Examples of adverbs
reasonably, rationally, ably, appropriately, acceptably, speculatively, simply, incessantly, interestingly, opaquely, suspiciously, secretly, shyly, slowly, sanely, selectively, persistently, perspicaciously, precipitately, pleasantly