To ask for permission use a verb + 도 + 되다 with a rising intonation :

여기 앉아도 돼요? = 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 or “to sit”. Since 앉다 uses an 아 vowel, the construction will use 앉아 instead of 앉어. Also, 되다 will become 돼요 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? = Can I eat this?

(이거 = this. 먹어 = eat. 도 돼 = can I)

The verb used here was 먹다, which has a 어 vowel. Therefore 먹다 will be conjugated as 먹어 rather than 먹아. 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.

You can also prohibit people from doing something by using a verb + (으)면 안되다

Take a look at these two sentences :

(1) 거기 집을 지으면 안 돼요 = 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 = 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 (to build) and the verb used in the second sentence was 세우다 (to park). Since the verb in the first sentence ended in a consonant (when the 다 of the infinitive was dropped), 으면 안 돼요 was used. However the verb in the second sentence ended in a vowel, which means that just 면 안 돼요 was needed. When the verb ends in a consonant, add 으. When it ends in a vowel, 으 is not needed.