What is the difference between 는/은 and 이/가 ?Feel free to just provide example sentences.

은/는 is called 보조사(auxiliary postpositional particle - A postpositional particle that is attached to a substantive, adverb, conjugational verbal ending. It’s used to add a special meaning to the word.)
이/가 is called 격조사(case-marking postpositional particle, and actually 이, 가 is a subject case marker(which shows its a subject of the sentence)
Also 격조사 can be deleted in a sentence because Koreans have no problem with understanding the sentences without it.(because they usually don’t have special meanings)
However 보조사 contains a meaning, so you can not erase it. (In case of 은/는 it has a meaning of comparing something, or to empathize noun.
ex) 여름이 좋아요.(I like summer.)
여름은 좋아요.( I like summer.. but)
여름이 좋지만 겨울은 싫어요.(X)
여름은 좋지만, 겨울은 싫어요.( I like summer but I hate winter.)
Hope it helped U:)