An adverb is a word which describes a verb, a bit like how an adjective describes a noun (not a ‘jective’, which would be cooler and make more sense but whatever I don’t even care).
For example, most adverbs in English are those words which end in ‘ly’, like ‘chaotically’, ‘horizontally’ or ‘quickly’. You use them to describe an action, such as ‘to drive chaotically’, ‘to spread out horizontally’ or ‘to disintegrate quickly’.
In German, life is even easier. Adverbs are almost always identical to the corresponding adjective, but to indicate that the word is describing a verb, there is no adjective ending added. For example:
Wir gehen schnell zur Bank, ok?
Sie fährt immer ganz chaotisch.
Musst du aber so laut essen??