Learn Hardcore Korean: ellibeiteoga gyedan yeope seolchidoeeosseoyo. - An elevator was installed next to the stairs.

가 is the subject marker. It attaches to a noun ending in a vowel (like 엘리베이터) and tells you that this noun is the subject of the sentence. If the noun ended in a consonant, you’d use 이 instead.

Why is the verb 설치되었어요 used instead of 설치했어요?

설치하다 (to install) is the active verb.
설치되다 is its passive form (to be installed).
설치되었어요 → 설치되다
- past tense -었어요 = “was installed” (focuses on the elevator receiving the action).
If you wanted to say “I installed it,” you’d use 엘리베이터를 설치했어요 (active voice).

What’s the function of 옆에 in 계단 옆에?

옆 means “side.”
Adding 에 marks a static location.
계단 옆에 literally means “at the side of the stairs,” i.e. “next to the stairs.”

Could you use 옆에서 instead of 옆에 here?

옆에서 often marks the place where an action takes place (“do something from/by the side”).
Since 설치되었어요 describes a state/result (the elevator now exists there), you use 옆에 for location.

Why isn’t 계단 marked as plural (with 들) to mean “the stairs”?

Many Korean nouns don’t need a plural marker when the meaning is clear. 계단 inherently refers to a set of steps, so adding 들 is unnecessary and uncommon.

Can you omit 엘리베이터가 and just say 계단 옆에 설치되었어요?

Yes. Korean often drops the subject when it’s understood from context. You’d still understand “It (the elevator) was installed next to the stairs.”

Is the word order fixed here? Could you say 계단 옆에 엘리베이터가 설치되었어요?

Korean word order is relatively flexible because of particles. Both
• 엘리베이터가 계단 옆에 설치되었어요
• 계단 옆에 엘리베이터가 설치되었어요
mean the same thing. The choice depends on what you want to emphasize first.

What about the contracted form 설치됐어요? Is it the same as 설치되었어요?

Yes. 설치됐어요 is simply the common contraction of 설치되었어요 (the vowel 이 + 었 contracts). It’s widely used in both spoken and written Korean and means exactly the same thing, just a bit more casual.