Ok - so we have the basics down but what else is there to know? In addition to marking topics, 은/는 has the nuance of 'about' something. For example: 1) 이거 사과예요. = This is an apple. You can add 은/는 to this, and in this case the subject, 이거, ends in a vowel, so add -는. 이거는 사과예요. = (The other things are not apples, but) THIS is an apple. 2) 이거 커피예요. = This is coffee 이거는 물이에요. = (That was coffee, but THIS ONE) it’s water. Although 은/는 are topic marking particles, people often save 은/는 for really emphasizing the topic in contrast to the other parts of the sentence. For example, if you want to say “The weather’s nice today.” in Korean, you can say it in many ways. 1) 오늘 날씨 좋네요. The weather’s good today. 2) 오늘은 날씨 좋네요. The weather’s good today. (The weather hasn’t been so good lately, but TODAY, it’s good.) 3) 오늘 날씨는 좋네요. The weather’s good today. (Today, not necessarily everything else too, but at least the weather is good.) This is how big the nuance is.