Adverbs add information to verbs, but also to adjectives, another adverb or even a whole sentence.

They often end in –ly.

Adverbials are other words or even phrases acting as adverbs.

Adverb(ial)s of manner tell how something is done: quickly, enthusiastically, “without even looking”.

Adverb(ial)s of place tell where something occurred: here, away, “in the library”.

Adverb(ial)s of time tell when, for how long or how often something occurred: soon, briefly, “a week last Tuesday”.

Adverb(ial)s of degree tell to what degree something is/was: very, hardly, incredibly.

Sentence adverbs qualify the whole sentence rather than just the verb, e.g. “Hopefully, he’ll arrive soon” – this doesn’t mean that he will arrive in a hopeful state, but that the speaker hopes he’ll arrive soon.  Therefore, sentence adverbs are particularly useful when you need to look at writer/audience positioning or attitudes in a text.  If someone starts a sentence with ‘clearly’ or ‘obviously’, for example, they make it very hard for a reader to take a different view.