Learn Hardcore Korean: hyeongwaneseo chingureul gidaryeoyo.

현관 means “entrance,” “foyer,” or “hallway,” typically referring to the front entrance of a house or building. The particle 에서 marks the location where the action takes place. So 현관에서 translates to “at the entrance.”

Why do we use the particle 에서 here instead of 에?

에서 is used to indicate the place where an action occurs (dynamic location). By contrast, 에 can mark a static location or a destination. Since 기다리다 (“to wait”) is an action happening at that spot, you need 에서.

Why is 친구를 marked with 를 rather than with 가?

In Korean, 를/을 is the particle for a direct object—the entity that receives or is affected by the verb. Because you “wait for” your friend, 친구 is the direct object of 기다리다, so you attach 를.

What level of politeness and tense is conveyed by 기다려요?

기다려요 is the present tense informal polite form (often called “-요 form”) of the verb 기다리다. It’s the standard conversational level you’d use with people you’re not extremely close with, but still polite.

Could I express this sentence in the progressive aspect, like “I am waiting”?

Yes. To emphasize that the waiting is in progress right now, you can say:
현관에서 친구를 기다리고 있어요.
Both forms are correct; 기다리고 있어요 highlights that the action is ongoing.

Why is there no subject before 현관에서? Can I add 저는?

Korean often omits the subject when it’s clear from context. If you want to explicitly state “I,” you can add 저는. The most natural placement is at the beginning:
저는 현관에서 친구를 기다려요.

What is the typical word order in this sentence?

Korean generally follows Subject–(Time)–(Location)–Object–Verb. Here it breaks down to:
(저는) 현관에서 친구를 기다려요.
[Subject/Topic] [Location] [Object] [Verb]

Can I change 현관에서 to another place, such as 학교에서?

Absolutely. Just substitute the location and keep 에서 for actions:
학교에서 친구를 기다려요. (“I’m waiting for my friend at school.”)