많이 means 'a lot' and attached before a verb and endings, like 많이 주세요 means "give me a lot of it" 아주 means "too" and used in front of a sentence, like 아주 뚱뚱해요 means "too fat" 너무 means "very or really" used before a verb, 너무 좋아요 means "it's really good" :)