Learn Hardcore Korean: hakgyo oenjjoge kapega isseoyo. - There’s a café on the left side of the school.

The particle -에 marks a location where something exists or an action takes place. In 왼쪽에, it turns 왼쪽 (left side) into “at/to the left,” indicating where the cafe is located.

Why do we use 있어요 in this sentence?

있어요 is the polite form of the verb 있다, meaning “to exist” or “to have.” Here it expresses existence: “There is a cafe.” It doesn’t show possession, but simply states that the cafe exists at that location.

Why is 카페 followed by the subject marker 가?

In Korean, the thing that exists (or performs an action) is marked with the subject particle 가 (or 이 after a consonant). 카페가 tells us that the cafe is the subject of 있어요, i.e. it’s what exists at 학교 왼쪽에.

Can we use the topic marker 는 instead of 가 with 카페?

Yes, you can say 카페는 있어요, but this shifts 카페 into the topic position and adds a contrastive or known-information nuance: “As for the cafe, it exists.” With 가, you’re simply stating existence without that nuance.