-더니 can have two meanings. 1) (in present tense) X-더니 Y => one thing happens first and then another follows (in a way that leaves a strong impression on the observer). This usually describes a third person or thing, not what you do yourself. (sometimes it can indicate cause-and-effect connection, but not always) - 사흘 동안 춥더니 오늘은 따뜻하다" = It's been cold for three days, but it's warm today. - 동생은 밤 늦게까지 놀더니 10시가 되도록 자고 있다 = My brother stayed up playing late into the night, and now at ten, he's still sleeping. 2) (past tense) X-ㅆ더니 Y => indicates one doing thing has caused another, or one things is followed by another (as in #1). This is typically used for the first person. - 아이 머리를 쓰다듬어 줬더니 좋다고 웃는다 = I stroked the child's head and he's smiling happily. - 인터넷 연결이 안 돼서 라우터를 리셋시켰더니 된다 = I couldn't connect to the Internet, so I reset the router and it's working. -더니만 is similar. It just adds emphasis by contrasting the first and second part more sharply.