은 는 – Topic markers or topic marking particles

이 가 – Subject markers or subject marking particles

은 는 indicates the topic of the sentence and 이 가 indicates the subject of the sentence. The grammatical subject is related to 이 가. The fun fact is many native speakers frequently omit these particles in daily conversation

If the word ends with consonants we use 은 or 이
이것은, 이것이 – This is
저것은, 저것이 – That is

If the word ends with vowels we use 는 or 가.
저는, 제가 – (I’m) formal

나는, 내가 – (I’m) informal

When to use 은 는

In simple sentence