Learn Hardcore Korean: japangieseo keopireul sayo. - I buy coffee at the vending machine.

에 marks a static location or existence: e.g., 자판기에 커피가 있어요 (There is coffee in the vending machine).
에서 marks the place where an action occurs: buying happens at the vending machine, so 에서 is correct.

Does 에서 here mean “at” or “from”?

Both are possible nuances:

“at” = the place of the action.
“from” = the source you buy it from. With 사다 (to buy), English can be either “at” or “from,” and both match 에서.

Why is it 를 and not 을 after 커피?

Use 를 after a vowel and 을 after a consonant.

커피 ends with a vowel → 커피를.
If it were 물 (water), you’d say 물을.

Where is the subject? Who’s buying?

Korean often omits the subject when it’s obvious from context. By default, it’s understood as “I” in a neutral context. You can add one for clarity:

저는 자판기에서 커피를 사요. (As for me, I buy…)
Or use a name, e.g., 민수는…

What politeness level is 사요? What are other options?

사요: informal polite (most common in daily conversation).
More formal: 삽니다.
Casual plain to friends: 사 or 산다 (diary/written).
To address someone respectfully or make a polite request: 사세요 (can be “Do you buy?” honorifically or “Please buy,” depending on context).

What tense is 사요? Can it also mean a near-future plan?

Non-past in Korean covers present, habitual, and near-future:

Present/habitual: “(I) buy,” “(I) buy (regularly).”
Near-future (depending on context): “(I’m) going to buy.”
Explicit past: 샀어요.
Ongoing: 사고 있어요.
Planned future: 살 거예요.

Can I change the word order?

Yes, as long as the verb stays at the end.

커피를 자판기에서 사요 is also natural. Word order changes can add emphasis to the moved element, but meaning stays the same.

Can I drop particles like 를 or 에서?

Dropping 를 is common in speech: 자판기에서 커피 사요.
Keep 에서 to avoid ambiguity. Without it, 자판기 커피 사요 tends to mean “I buy vending-machine coffee (as a type)” rather than clearly stating the location/source.

If I add a subject, should it be 저는 or 제가?

저는 (topic): neutral, sets “me” as the topic. 저는 자판기에서 커피를 사요.
제가 (subject): emphasizes that it’s specifically “I” (as opposed to someone else). 제가 자판기에서 커피를 사요.

What’s the difference between 커피는 사요 and 커피를 사요?

커피를 사요: neutral “(I) buy coffee.”
커피는 사요: contrastive/topic “As for coffee, (I) do buy (it)”—implies contrast (maybe you don’t buy tea, etc.).

How do I say “I buy one cup of coffee at the vending machine”?

Most natural: 자판기에서 커피 한 잔(을) 사요. (object marker after the classifier is common but often dropped in speech)
Also possible: 자판기에서 커피를 한 잔 사요.

How would I ask this as a question?

Polite: 자판기에서 커피를 사요? (intonation or question mark makes it a question)
To ask someone respectfully (honorific subject): 자판기에서 커피를 사세요?
About a plan: 자판기에서 커피를 살 거예요?

Any natural variations or synonyms?

With the vending-machine verb: 자판기에서 커피를 뽑아요 (“I get coffee out of the vending machine”); or 뽑아 마셔요 (“get it and drink it”).
More formal word for the machine: 자동판매기.
Talking about the type: 자판기 커피(를) 사요 (“I buy vending-machine coffee”).

Can I use 한테/에게/으로부터 instead of 에서?

Not here. 한테/에게/에게서/한테서/으로부터 are for sources that are typically animate (people, organizations). With an inanimate source/place like a machine, use 에서.

How do I say it in the past or negative?

Past: 자판기에서 커피를 샀어요.
Simple negative: 자판기에서 커피를 안 사요.
Formal/long negative: 자판기에서 커피를 사지 않아요.

Any quick pronunciation tips or romanization?

Romanization: 자판기에서 커피를 사요 → japangi-eseo keopi-reul sayo.
에서 sounds like “e-seo”; 를 is pronounced “reul” after a vowel.
In connected speech, words link: 커피를 사요 may sound like “커피를사요.”