An adverb characterizes a verb. It answers a question How? Как ты это делаешь? How do you do it? Я делаю это хорошо. I do it well. Хорошо – is an adverb.
An adverb doesn’t change its form.
Note:
Do not mix an adverb with an adjective.
An adjective characterizes a noun. Я читаю хороший рассказ. I am reading a nice story. Хороший is an adjective.
An adverb characterizes a verb. Я читаю хорошо. I read well. Хорошо is an adverb.