An adverb can be added to a verb to modify its meaning. Usually, an adverb tells you when, where, how, in what manner, or to what extent an action is performed.
Many adverbs end in ly — particularly those that are used to express how an action is performed.
Although many adverbs end ly, lots do not, e.g., fast, never, well, very, most, least, more, less, now, far, and there.