Learn Hardcore Korean: gyedaneseo chingureul gidaryeoyo.

The particle 에서 marks the location where an action occurs (“at/on the stairs”). 에 alone often indicates a static location or movement target (“to the stairs”). Since 기다려요 (“wait”) is an action taking place there, you use 에서.

What role does 를 play in 친구를 기다려요?

를 is the object-marking particle. It tells you that 친구 is the direct object of the verb 기다리다 (“to wait for”). Without 를, the sentence would be ambiguous.

There’s no word for “I” in this sentence. Where is the subject?

In Korean, the subject is often omitted when it’s clear from context. Here, 저/나 (“I”) is implied. If you need to be explicit, you can say 저는 계단에서 친구를 기다려요.

Why does the verb end with -요, as in 기다려요?

The -요 ending is part of the polite informal speech level (해요체). It’s common in everyday conversation with strangers, coworkers, or acquaintances. For a more formal style you’d say 기다립니다, and for very casual speech with close friends or younger people you might drop -요 entirely.

How would I say “I’m waiting” if I want to emphasize that it’s happening right now?

Use the progressive form 기다리고 있어요.
Full sentence: 계단에서 친구를 기다리고 있어요.
That stresses “I’m in the middle of waiting” rather than just “I wait.”

Why is 친구를 placed before the verb instead of after, like in English?

Korean follows Subject-Object-Verb (SOV) order. Place the object (marked by 를) before the verb. The order of time and place phrases is flexible, but the verb always comes at the end.