-은/는/을 것 같다 is a grammar pattern for supposition
Verb stem+(으)ㄴ : past tense
e.g.
먹다 -> 먹은
가다 -> 간
Verb stem+는 : present tense
e.g.
먹다 -> 먹는
가다 -> 가는
Verb stem+(으)ㄹ : future tense
e.g.
먹다 -> 먹을
가다 -> 갈
Literally, 것(과) 같다 means "It is same thing that"
그는 사과를 먹은 것 같다 It is same thing that he ate an apple. => It seems that he ate an apple.
그는 사과를 먹는 것 같다 It is same thing that he eats an apple. => It seems that he eats an apple.
그는 사과를 먹을 것 같다 It is same thing that he will eat an apple. => It seems that he will eat an apple.
Adjective stem+(으)ㄴ : past and present tense
e.g.
예쁘다 -> 예쁜
좋다 -> 좋은
Adjective stem+(으)ㄹ : future tense
e.g.
예쁘다 -> 예쁠
좋다 -> 좋을
e.g.
오늘 날씨가 좋은 것 같다. It seems that the weather is good today.
내일 날씨가 좋을 것 같다. It seems that the weather will be good tomorrow.