Some ㅅ ending verbs like 짓다 (to build) are a part of a special class of verbs that end in ㅅ.

In the standard polite present tense form, 짓다 will be conjugated as 지어요.

The 다 from 짓다 is dropped and so is the ㅅ from 짓. Then 어요 is added.

Let’s try conjugating the same for 낫다 (to get better from an illness)

Drop the 다 and the ㅅ. Then add 아요.

The complete version will be 나아요 in the presente tense of the standard polite form.

The vowel in 짓다 is an 이 vowel. This means that 짓다 will have an 어요 ending.

However, the vowel in 낫다 is 아, which means that 낫다 will have an 아요 ending.

The adjective 낫다 is spelled the same as the verb 낫다 but means something totally different.

The adjective 낫다 means “to surpass”, “be better than”, “be preferable to”

The way you can tell the difference in meaning is by the context of the sentence.

The present tense of the deferential polite of 짓다 is 짓습니다.

Drop the 다 and just add 습니다.

If you do the same for 낫다, you get 낫습니다.

In the present tense of the honorific polite, 짓다 will be 지으세요.

Drop the 다 and ㅅ in 짓다 and add 으세요.

Do the same for 낫다 and you get 나으세요.

Just so you know, not all ㅅ ending words belong to the same category of 짓다 and 낫다.

For example, 벗다 (to take one’s clothes off) does’t belong to the category that 짓다 and 낫다 belong to.

In the standard polite present tense 벗다 will be conjugated normally as 벗어요.

Notice that the ㅅ in 벗다 isn’t dropped like the ㅅ in 짓다 or 낫다.