"-가" is a subject marker meaning it makes a noun into a subject like "-が" in "김치 + が + おいしい" in Japanese.^^/ "-이" is used when a noun ends with a last consonant(=받침) instead. e.g. 꽃(=flower) 꽃이 예쁘다.("ㅊ" in "꽃" is a last consonant, that's why "이" is used) \^o^/

it‘s just a particle with no meanings to show that 김치 is the subject of the sentence. There are lots kinds of particles in Korean and I think that is what makes Korean difficult!