One of the most frequent mistakes for Italian learners is mixing up "bene" and "buono". Here is the simplest way to tell them apart:
BUONO (ADJECTIVE)
Buono means "good." It is an adjective, which means it describes nouns (people, places, or things). Because it’s an adjective, it must change to match the gender and number of what you are describing.
“Questo piatto è buono” (This dish is good)
"È un'idea molto buona!" (It’s a very good idea!)
BENE (ADVERB)
Bene means "well." It is an adverb, which means it describes verbs (actions). It tells you how something is done. Unlike buono, bene never changes its form — it is always the same.
E.g.:
"Parlo bene l'italiano" (I speak Italian well)
"Sto bene, grazie" (I am [doing] well, thank you)
“Suono la chitarra abbastanza bene” (I play the guitar quite well)
A common trap: In English, you often say "I'm good" when someone asks how you are. In Italian, if you say "Sono buono" you are actually saying "I am a good/moral person." If you want to say you are feeling healthy or happy, you must say "Sto bene".