Let's learn how to use "Adj+ (으)ㄴ 것 같다 [Korean grammar]" and make some example sentences.

CONJUGATION RULE:

Adj+ (으)ㄴ 것 같다 grammar is used with adjective. The first step of ‘Adj+ (으)ㄴ 것 같다’ conjugation is to remove ‘다’ from the base form of the adjective.

• If the adj. stem is ending with a final consonant (받침), we use 'Adj+ 은 것 같다'.
• If the adj. stem is ending with any vowel( without patchim) then 'Adj+ㄴ 것 같다' is used. 

So let's take an adjective 바쁘다(to be busy). If you remove 다 from 바쁘다, 바쁘 (stem) is left. So in the 바쁘, is ending without final consonant i.e. Patchim.

According to the conjugation rule, if the stem ends without Patchim, we add-ㄴ 것 같다.

So it becomes 바쁜 것 같다.

So, if you want to say- "He looks busy/It seems like he is busy." 

Then, you'll say- "바쁜 것 같아요."

EXAMPLE SENTENCES:

• 이 책이 비싼 것 같아요.
  (This books seems expensive.)
• 날씨가 너무 추운 것 같아요.
  (The weather seems really cold.) 
• 물을 진짜 따뜻한 것 같아요.
  (The water seems really warm.)
• 미나 씨가 피곤한 것 같아요.
  (Mina seems like tired.)
• 앤디 씨 머리가 아픈 것 같아요.
  (It looks like Andy is having headache.)

"Adj+ (으)ㄴ 것 같다" can be used in the present, past and the future:

Let's take a common example to understand it better.

" 바쁘다- To be busy" 

Now let's make the same sentences in present, past and future tenses.

-은/ㄴ 것 같다- PRESENT TENSE:
Example:

• 앤디 씨가 바쁜 것 같아요. (It seems like Andy is busy.)

-았던/었던 것 같다- PAST TENSE:
Example:

• 앤디 씨가 바빴던 것 같아요. (It seems like Andy was busy.)

-ㄹ/을 것 같다- FUTURE TENSE:
Example:

• 앤디 씨가 바쁠 것 같아요. (It seems like Andy will be busy.)