The subject markers in korean are 이/가. These are used more often than 은/는. 이 is used with verbs ending with consonants while 가 is used with verbs ending with vowels. Don't mix this particle -가 with the verb 가다. Those are both two different things.

A subject marker is used to show what's the sentence about. Just like,

날씨가 좋아요!

The is good! / I like the !

뭐가 좋아요?

good? / do you like?

그 카페가 너무 예뻐요.

That is very pretty.

네, 그 선물이 완전 커요.

Yes, the is totally big.

It can also be used to emphasize on a certain word in the sentence.

A: 야 정민아! ABC 어때요? 좋아요?

Hey Jeongmin! How's ABC? Do you like it?

B: 아니요, 안 좋아요. XYZ가 또 예뻐요.

Nahh, I don't like it. XYZ is prettier (more pretty).

A: 아 그래요?

Oh is that so?

B: 네 그렇게 생각해요

Yeah I think so.

Remember the word 누가 that mysteriously changed from 누구 to 누가 ?

Its construction is something like 누구 → 누 + 가 (subject marker) → 누가.

That's it for today, 안녕♡