One thing to look for is that adverbs often (but not always) end with -ly, as in HarryT's “quickly.” Not all words that end with -ly are adverbs, either (“We hung the holly for Christmas”). But it's a hint.
Adverbs can modify verbs as HarryT says. They can also modify adjectives (“You are
mostly right”), other adverbs (“He walked
quite slowly”), phrases/sentences, and even nouns and noun phrases (“There is a shortage
internationally of protein for animal feeds”).
If you're having trouble pinning them down, you can take solace in the fact that modern grammarians view “adverb” as more of a catch-all category than a strict part of speech, as they really serve a number of different purposes that are lumped together. To some extent they can be viewed simply as non-adjectival modifiers, and it can be easy to conflate the two:
- Even camels need to drink. (“Even” is an adverb)
- Even numbers are divisible by two. (“Even” is an adjective)
As Wiki says: Adverbs typically express manner, place, time, frequency, degree, level of certainty, etc., answering questions such as
how?,
in what way?,
when?,
where?, and
to what extent?