You have been using this since your first sentence:
저는 학생이에요.
은/는 puts a noun up front and says: *this is what I am talking about.* English often reaches for “as for…”.
저는 커피를 마셔요. — As for me, I drink coffee.
Same split, one more time
은 after a consonant · 는 after a vowel
선생님은 · 저는
Do not worry yet about 은/는 versus 이/가. That comparison is real, and it has a whole course of its own later. Right now one habit carries you a long way: use 은/는 on the person or thing your sentence is about, usually at the very front.
저는 한국 사람이에요.As for me, I am Korean.
제 동생은 학생이에요.My younger sibling is a student.
오늘은 시간이 없어요.Today, I have no time. 은/는 can mark time too — “as for today”.
It also does contrast
Put 은/는 on two things and the sentence sets them against each other.
커피는 좋아해요. 그런데 차는 안 좋아해요. — I like coffee. But tea, I don’t.
연습 · Practice
이 레슨에는 풀어 보는 문제가 6개 있습니다. 앱에서 하나씩 맞히며 넘어갑니다. 6 exercises come with this lesson — open it to work through them.