Have you ever confused good with well? The difference is subtle: one is an adjective and the other is an adverb. To recap, adjectives modify nouns whereas adverbs modify verbs, adjectives, and other adverbs.
But you don’t have to be a pro at figuring out if a word is modifying nouns, verbs, adjectives, etc… Just replace the word in question something you know is an adjective or adverb and see how it sounds.
To practice, let’s use beautiful and beautifully.
Let’s try one more:
