Answer:
은/는 is subject particle and it varies to syllables in a subject noun. For example if the noun ends with vowel the particle forms 는. But if it ends with consonant (or let's say Batchim: 받침) the particle forms 은.
e.g.
저는 (I am)
여기는 (Here is)
저기는 (there is)
이것은(this is)
저것은(that is)
제 이름은 (my name is)
