Adverbs are words that provide additional information about verbs, adjectives, or other adverbs and are usually placed next to the words they describe. They can be formed from adjectives by adding '-ly', though some adverbs share the same form as adjectives and do not take the 'ly' ending. Adverbs can specify manner, time, or place, answering questions like how something is done, when it happens, or where it is located.