~어/아/여도 되다 – (it’s okay even if..), allowed to, it’s okay if..

되다 – can, to be possible, to function
지금 인터넷 돼요? – Does the Internet work now? 
배달 돼요? – Can you deliver it?

여기 앉아도 돼요? – Is it all right if I sit here? 
이거 먹어도 돼요? – Do you mind if I eat this? 
돈 좀 빌려도 돼요? – Would it be all right if I borrowed some money?
먼저 먹어도 돼요? – Would you mind if I went ahead and ate?
이거 써도 돼요? – Would it be all right if I used this?

내일 해도 돼요 – It’s okay if you do it tomorrow. You can just do it tomorrow
네, 써도 돼요 – Yes, you can use that.
TV 봐도 돼요 – You are allowed to watch TV
이 케잌 먹어도 돼요 – You can eat this cake
어제까지 놀아도 됐었어요 – Until yesterday, I was allowed to muck around.
맛이 없으면 안 먹어도 돼요 – If it’s not tasty, it’s okay not to eat it.

or ~아/어도 괜찮다 – it’s alright to, okay to  (this is less direct/more polite!)

지하철을 타도 괜찮아요? – Is it alright to take the subway?
네, 지하철을 타도 괜찮아요 – Yes, it is alright to take the subway.

안 ____ 어/아도 되다  – don’t have to, it’s okay even if you don’t

안 해도 돼요 – You don’t have to do it. It is okay if you don’t do it.
안 먹어도 돼요 –  You don’t have to eat it. It’s okay if you don’t eat it

~아/어/여도 될까요? – i wonder if it’s okay if i..

 ~(으)면 안 되다, 안됐었다 – can’t, shouldn’t, not allowed (it’s not okay if..)  

아니요, 내 휴대폰 쓰면 안 돼요 – No, it’s not all right for you to borrow my phone
아니요, 거기 앉으면 안 돼요 – No, you can’t sit down there
아니요, 먼저 먹으면 안 돼요 – No, you shouldn’t just go ahead and eat
술과 담배는 사면 안돼요 – You are not allowed to buy alcohol and tobacco
작년까지 빅토리아공원에는 들어가면 안됐었어요 – Until last year, people were not allowed to enter the Victoria park
고양이 만지면 안 돼요 – You’re not supposed to touch the cat.
지금 가면 안 돼요 – You shouldn’t go now.
아직 먹으면 안 돼요. 아직 뜨거워요 – You should eat yet. It’s still hot.