은/는 is for 3 ceases 1. when you describe something ex) 거북이는 아프다 = a turtle is sick 방은 깨끗하다 = a room is clean 2. when you define something ex) 이것은 책이다 = this is a book 저것은 가방이다 = that is a bag 3. when you introduce something or someone ex) 이 남자는 한국인 입니다 = this man is a Korean 저 여자는 미국인 입니다 = that woman is a American you can use also 이/가 instead of 은/는 and meaning is same but 이/가 is for when you emphasizing something ex) 거북이가 아프다 = the turtle is sick 방이 깨끗하다 = the room is clean and about 을/를 is for the objective case ex) 어머니는 빵을 먹는다 = the mother is eating a bread 아버지는 책을 읽는다 = the father is reading a book I hope my explanation would help ^^

You use 는/은 as a topic particle, and 을/를 for as an object particle. Let me give you an example: 저는 사과를 먹었어요. = I ate an apple. 저 = I 사과 = apple 먹다 = eat (in this example, 먹었어요 is the past tense form of "eat", so it would be "ate") In this case, because "저" is the topic, then it also is the subject. It means that "저" is the one who "먹었어요" ("I" am the one who "ate"). "사과" is the object because it is what I ate. The apple is not eating. It is just the object that I ate. So we use 를 to indicate it is the object. I hope that my explanation makes sense to you?

I believe 는 and 를 are used when the noun/object ends in a vowel. The other two are used when they end in consonants