Learn Hardcore Korean: geosil jomyeongeul kyeogo yeonghwareul bwayo. - I turn on the living room light and watch a movie.

-고 links two actions by the same subject. It can mean simple “and,” but in many cases (like this one) it implies the first action happens and then the second happens.
Here, the natural reading is: turn on the living room lights, and then watch a movie. It also easily implies the lights stay on during the movie.
If you want to strongly emphasize “after doing A, do B,” you can say -고 나서: 거실 조명을 켜고 나서 영화를 봐요.
If you want to express “while,” use -면서 for overlapping actions: e.g., 음악을 들으면서 영화를 봐요.

Why is there no subject? Who is doing the actions?

Korean often omits the subject when it’s clear from context. Here, the subject is understood as “I” or “we.” You can add one if needed:

저는 거실 조명을 켜고 영화를 봐요. (I…)
우리는 거실 조명을 켜고 영화를 봐요. (We…)

What politeness level is 봐요? Is the sentence polite?

봐요/켜요 are in the standard polite style (-아요/어요), suitable for everyday conversation with most people.
More formal: 봅니다/켭니다.
Casual: 봐/켜 (to friends, younger people).
Honorific for a respected subject (not yourself): (으)시. For example, 할머니께서 영화를 보세요.

Why is it 거실 조명 and not 거실의 조명?

Both are grammatical. In everyday speech, 의 is often dropped, and a noun directly modifies another noun: 거실 조명 = “living room lighting.”
거실의 조명 can sound a bit more formal or bookish.
Very natural and colloquial is also 거실 불 (“the light(s) in the living room”).

Can I say 거실 불을 켜고 instead of 거실 조명을 켜고?

Yes. 불 is very common in daily speech for “light(s),” while 조명 can feel more general or technical (the lighting/illumination). You can also hear 전등을 켜다 (“turn on the lamp/light”).

Should there be 에서 to mark the place of watching? Where is the movie watched?

The sentence doesn’t specify the location of watching; it only mentions the lights are in the living room. If you want to say you watch in the living room:

거실 조명을 켜고 거실에서 영화를 봐요. If location isn’t important, the original is fine.

What do 을/를 do in 조명을/영화를? Why 을 for one and 를 for the other?

을/를 mark the direct object.
Use 을 after a noun ending in a consonant sound: 조명(을).
Use 를 after a noun ending in a vowel sound: 영화(를).

Can I drop 을/를 here?

Yes, in casual speech it’s common to drop object markers when the meaning is clear:

거실 조명 켜고 영화 봐요. With multiple objects, keeping them can help clarity, but dropping them here is very natural.

Does -고 here mean I keep the lights on while watching?

It easily suggests that: “turn the lights on and (then) watch” implies the lights remain on. If you want to make “leave them on” explicit, use:

거실 조명을 켜 놓고 영화를 봐요.
거실 조명을 켜 둔 채로 영화를 봐요.

What’s the difference between 켜다 and 틀다?

켜다 is the default for turning on lights, screens, or devices: 불을 켜다, TV를 켜다, 컴퓨터를 켜다.
틀다 is commonly used for devices like TV/radio/music/aircon in some regions and contexts: TV를 틀다, 라디오를 틀다, 에어컨을 틀다. For lights, stick with 켜다.

Is 보아요 correct? How is it related to 봐요?

봐요 is the standard contraction of 보아요 (from 보다 + -아요).
Both are correct; 봐요 is what you’ll normally see and say.

How do I say this in the past, future, or ongoing present?

Past: 거실 조명을 켜고 영화를 봤어요. (Only the last verb shows past; that’s normal.) You could also list both in past: 거실 조명을 켰고 영화를 봤어요, which sounds like two completed actions in sequence.
Future: 거실 조명을 켜고 영화를 볼 거예요.
Ongoing (right now): 거실 조명을 켜 놓고 영화를 보고 있어요.

Is there a difference between -고 and -아서/어서 here?

Yes.

-고: neutral linking/sequence (“and/then”).
-아서/어서: cause or reason (“so/because”). 거실 조명을 켜서 영화를 봐요 implies “I turn on the lights so (that) I can watch a movie,” which can be fine but carries a causal/purposeful nuance.
For explicit purpose, use -(으)려고: 영화를 보려고 거실 조명을 켜요.

Could I change the order to 영화를 보고 거실 조명을 켜요?

Grammatically yes, but it changes the meaning to “I watch a movie and then turn on the living room lights,” which is odd in real life. Word order with -고 directly affects the sequence you’re implying.

How can I say “one movie” or “a couple of movies”?

Use counters:

One movie: 영화 한 편(을) 봐요.
Two movies: 영화 두 편(을) 봐요. You can insert these into the sentence: 거실 조명을 켜고 영화 한 편을 봐요.

Any pronunciation tips for this sentence?

켜고: be sure it’s “kyeo-go” (ㅕ like “yuh”), not “kyo-go.”
봐요: pronounced like “bwa-yo” (it’s the contracted form).
영화를: link smoothly as “yeong-hwa-reul.” Speak it naturally as: [거실 조명을 켜고 영화를 봐요].