"Well" is an adverb. "Good" is an adjective. If you don't know how adverbs and adjectives are used, then you need to study the eight parts of speech, which will teach you how to use adverbs and adjectives.

You use well to describe an activity such as "he can read very well" or "I can paint well" or you use it for health as in "she was doing very well but now her health is declining" or if someone asks how you are you reply "very well thank you" and good is used to describe an object such as "that painting is very good" or "This pasta is very good"