Giving/Denying/Asking Permission

To ask for permission use a verb + 도 (do*) + 되다 (Doeda*) with a rising intonation :
여기 앉아도 돼요? (YeoGi AnchADo Doeyo*) = Can I sit here? or Am I allowed to sit here?
(여기 = here. 앉아 = sit. 도 돼요 = can I/am I allowed.)

The verb used here was 앉다 (Ancha*) or “to sit”. Since 앉다 uses an아 (A*) vowel, the construction will use 앉아 (AnchA*) instead of 앉어. Also, 되다 (Doeda*) will become 돼요 (Dwaeyo*) when conjugated.

The phrase above was a polite way to ask for permission. You can also ask for permission in an informal way, though I’d be careful to use this with certain people :
이거 먹어도 돼? (IGeo MeokEoDo Dwae?*) = Can I eat this?
(이거 = this. 먹어 = eat. 도 돼 = can I)

The verb used here was 먹다 (MeokDa*) , which has a 어 (Eo*) vowel. Therefore 먹다(MeokDa*) will be conjugated as 먹어 (MeokEo*) rather than 먹아 (MeokA*) . By now, you probably have some intuitive sense that it’s 먹어 and not 먹아, just by the way it sounds. To ask in an informal way, just drop the 다 (A*) .

You can also prohibit people from doing something by using a verb + (으)면 안되다 [(Eu*)Myeon An Doeda*]

Take a look at these two sentences :
(1) 거기 집을 지으면 안 돼요 (GeoGi JibEul JiEuMyeon An Dwaeyo*) = You’re not allowed to build a house there
(거기 = there. 집 = house. 을 = obj. particle. 지 = build. 으면 안 돼요 = not allowed)
(2) 여기 차를 세우면 안돼요 (YeoGi ChaReul SeUMyeon AnDwaeYo*) = You(‘re) can’t/not allowed to park your car here
(여기 = here. 차 = car. 를 = obj. particle. 세우 = park. 면 안돼요 = not allowed/can’t)

The verb used in the first sentence was 짓다 (JitDa*) (to build) and the verb used in the second sentence was 세우다 (SeUDa8) (to park). Since the verb in the first sentence ended in a consonant (when the 다 of the infinitive was dropped), 으면 안 돼요 (EuMyeon An DwaeYo*) was used. However the verb in the second sentence ended in a vowel, which means that just 면 안 돼요 (Myeon An DwaeYo*)was needed. When the verb ends in a consonant, add 으 (Eu*). When it ends in a vowel, 으 (Eu*) is not needed.