Hi Arlette Leonor Ramirez, [을/를], [이/가], [은/는], [과/와] The first parts(을, 이, 은, 과) are applied when the last word has a final consonant. The second parts(를, 가, 는, 와) are applied when the last word does not have any final consonant. Ex. 나는 당신을 좋아해요. 나는 너를 좋아해. (I like you) 하늘이 맑다. (Sky is clear) 머리가 맑다. (I feel fresh) 어머님은 오늘 집에 계신다. 어머니는 오늘 집에 계신다. (My mother is at home today) 당신과 나는 잘 맞을거에요. 너와 나는 잘 맞을거야. (You and I will get along well) Hope it helps,

이/가 - subject case marker 을/를 - object case marker 은/는 - semantic marker (adding some special meanings to the noun phrase). It represents "topic or contrast." 은/는 sometimes is found in the location of the subject, that's why some people are confused. I suggest you should read many sentences in the context to get the difference. ^^