-것 같다 [ -geot gatda ]
같다 means usually ‘to be the same’. Polite forms are 같아요 [gatayo] or 같습니다 [gatseumnida].
너와 나는 나이가 같다. (You and me are at the same age.)
우리는 취미가 같아요. (We have the same hobby.)
However, -것 같다 is used to depict uncertainty or speaker’s guess. It is similar to the English expression ‘it seems -‘ or ‘I think -‘.
This expression usually comes after a verb or adjective, which ends with -ㄴ/는 for past or present and with -ㄹ/을 for future.
나 아픈 것 같아. (I think I am sick.)
눈이 온 것 같아요. (It seems it snowed.)
그가 올 것 같아요. (It seems he will come soon.)
그는 착한 것 같아요. (I think he is kind.) — the speaker probably had chances to see his kindness.
그는 착할 것 같아요. (I think he is kind.): the speaker does not know him very well or possibly saw him for the first time.