이/가 are subject marking particles. 이 used after words ending in a consonant and 가 is used after words ending in a vowel. for example, when you want to say "the weather is good" you can say "날씨가 좋아요" in which, you've used 가 to mark your subject which is 날씨 (ending in a last vowel) 은/는 are the topic marking particles. 은 used after words ending in a consonant and 는 is used after words ending in a vowel. for example, when you want to say " this book is expensive " you can say " 이 책은 비싸요 " so you've marked the topic " 책 " with the topic marking particle. as a translation for the Korean sentence, you can also have " as for this book, it's expensive " so the topic marking particle, give the meaning of " as for .... " to the sentence, and makes one part the topic of the sentence. 을/를 are object marking particles. 을 used after words ending in a consonant and 를 is used after words ending in a vowel. when you want to say " please watch this movie " you can say " 이 영화를 보세요 " and here the movie (영화) is the object marked by 를. For more information, you can check the links below: www.talktomeinkorean.com/lessons/level-2-lesson-2-%EC%9D%84-%EB%A5%BC-object-marking-particles/ www.talktomeinkorean.com/lessons/l1l9/