Learn Hardcore Korean: iri kkeutnamyeon jamsi swieoyo. - When work is done, I rest for a moment.

The particle -이 is the subject marker used after a noun ending in a consonant. Here 일 (work) is the subject of the intransitive verb 끝나다 (to end), so 일이 means “the work (is what) ends.”

What’s the difference between 일이 끝나다 and 일을 끝내다? Why not say 일을 끝내면?

일이 끝나다 uses the intransitive verb 끝나다 (“to end by itself”), so 일이 marks the subject: “the work ends.”
일을 끝내다 uses the transitive verb 끝내다 (“to finish something”), so 일을 marks the object: “(someone) finishes the work.”
Both can form a conditional clause, but the first focuses on the work itself ending, while the second focuses on someone completing the work.

What does 끝나면 mean, and how does the -면 ending work here?

끝나면 is made from 끝나다 (to end) + conditional -면, giving “if/when (it) ends.” In Korean, -면 can express:
• a condition (“if…”)
• a time clause (“when…”)

Why is it 끝나면 and not 끝나으면? How do I know when to use -면 vs. -으면?

General rule:
• If the verb stem ends in a vowel, attach -면.
• If it ends in a consonant, attach -으면.
Since 끝나- ends in the vowel -ㅏ, you drop -으 and get 끝나면.

What does 잠시 mean in this sentence? Are there other words with a similar meaning?

잠시 means “for a short time” or “briefly.” It’s an adverb modifying 쉬어요.
Similar adverbs include 잠깐, 조금, and 잠깐만, all indicating a short duration.

How is 쉬다 conjugated to 쉬어요, and why not 쉬어 or 쉐요?

The verb 쉬다 has the stem 쉬-.
In the polite present tense, you add -어요: 쉬 +어요 = 쉬어요.
쉬어 is the plain/informal present form.
쉐요 is an incorrect spelling—you always keep the ㅟ sound in 쉬어요.

Is 쉬어요 an imperative (a command) or just a statement? How would I say “please rest” or “let’s rest”?

쉬어요 is a neutral polite present tense: it can describe an action or serve as a gentle suggestion (“(we/you) rest”).
For a clear command, use 쉬세요 (“please rest”).
For “let’s rest,” you can use 쉽시다 (formal) or 쉬어요 with -읍시다: 일이 끝나면 잠시 쉽시다.

Who is resting in this sentence? The speaker, the listener, or someone else?

Korean often omits subjects when context makes them clear. Here, 쉬어요 could refer to “you,” “we,” or people in general (like a sign advising workers).
To specify, you can add a pronoun:
• 제가 쉬어요 (“I rest”)
• 당신이 쉬어요 (“you rest”)
• 우리가 쉬어요 (“we rest”)