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
It is used after a noun that ends in consonants.
It is used after a noun that ends in vowels.