V + ㄴ/는다면 is the conditional 'if V happens' or 'if you V'. This is different from V+(으)면*, which can be if or when. This expression is often used with -겠어요, -(으)ㄹ 거예요, and -(으)ㄹ 텐데.
The condition attached to ㄴ/는다면 should be contrary to reality or now, and the speaker implies that there isn't a huge chance of it happening.
나쁜 날씨가 계속한다면 경기를 연기 할 거예요.
If the bad weather continues the game will be postponed.
일년 동안 간다면 배로 세계에서 여행 할 거예요.
If I could travel for a year I would sail around the world.
복권에 당첨된다면 멋진 자동차를 사고 싶어요.
If I won the lottery, I would want to buy a fancy car.
10년 전 돌아간다면 더 열심히 공부하고 싶어.
If I were to go back to 10 years ago, I want to study even harder.
For nouns, use N + (이)라면:
내가 대통령이라면 모든 일이 휴일 될 거예요.
If I were president every day would be a holiday.
내가 너라면 친구한테 사과 할 거예요.
If I were you I would apologise to your friend.
유명한 배우이라면 지금보다 돈을 많이 벌 거예요.
If I were a famous actor I would earn a lot more money than I do now.
For adjectives use A (dictionary form) + 면:
배가 고프다면 일에 집중하는 것이 힘들어요.
If I'm hungry it's difficult to concentrate on work.
너가 무섭다면 아마도 다른 여화를 봐야 돼요.
If you're scared, maybe we should watch a different movie.