What Do Adverbs Modify?
An adverb is a word that modifies (describes) a verb (he sings loudly), an adjective (very tall), another adverb (ended too quickly), or even a whole sentence (Fortunately, I had brought an umbrella). Adverbs often end in -ly, but some (such as fast) look exactly the same as their adjective counterparts.
Tom is very tall.