An adverb is a word that describes the verb.
Ex. quietly, rambunctiously, deliciously
In German, many adverbs end in -weise or -lang.
Ex. teilweise (partly), minutenlang (minutes long).
Notice that although the first part of the word is a noun, the word in its entirety is not a noun, and thus the word is not capitalized.
There are words called Adjective-Adverbs that have the same form as each other. As in, Adjective-Adverb words can be either an adjective or an adverb.
Ex.
Sie ist stark --> She is strong --> 'stark' is used as an adjective that describes the noun: the girl.
Sie sieht mich stark an --> She looks at me strongly (translated literally) --> 'stark' is used as an adverb that describes the verb ansehen (to look at).
Comparative adverbs are used to compare two actions of things/people. Examples of comparative adverbs are 'faster' and 'louder.'
Formation: article and/or noun + verb + (adverb + -er)
Ex.
Arlene läuft schneller. --> Arlene runs faster. (than someone else who also runs)
Superlative adverbs are used to indicate the most extreme degree of quality of an action that is done by a group of things/people. For example, if I say that someone sings the loudest, they are the most extreme in terms of volume when singing compared to a group. Examples of superlative adverbs are 'fastest' and 'loudest.'
article and/or noun + verb + am + (adverb + -sten)
Ex.
Er singt am schönsten. --> He sings the most beautifully. (out of a group)
There are irregular forms of adverbs (regular, comparative, and superlative) that you would only really know by memorizing them. Here are a couple of the common ones.