Adverbs express relations of place, time, quantity, and manner, among others. Adverbs can accompany a verb, an adjective or another adverb, and they are said to modify the word they accompany. My feet are very big. It is a potentially dangerous situation.
Some adverbs exist as words on their own right.
The same occurs in Spanish. In the type of words they modify The first notorious difference between adverbs and adjectives is that they cannot modify the same type of words. Thus, adjectives can accompany and modify only nouns, because they are used to express qualities or traits of objects, animals, and people. However, adverbs can modify other types of words, such as verbs, adjectives and other adverbs. In the way they relate to the words they modify Adjectives in Spanish acquire certain properties of the words they accompany and they must change to express those properties.