The word very is classified as an adverb. It is used to modify adjectives or other adverbs, typically to emphasize their meaning.
For example, in the phrase very tall, the word very enhances the adjective tall, indicating a greater degree of height. Similarly, in very quickly, it modifies the adverb quickly, reinforcing the rapidity of the action.
In essence, very serves the purpose of intensifying the quality described by the words it modifies, making it a useful tool in expressing emphasis in speech and writing.