ojeon sueobi kkeutnago naseo jeomsimeul meogeoyo.

오전 literally means before noon or A.M.

So 오전 수업 means a morning class or class in the morning.
It contrasts with 오후 for afternoon / P.M.

• 오전 = morning, before noon
• 오후 = afternoon, after noon

수업 is commonly translated as class, lesson, or instruction, depending on context.

In this sentence, 오전 수업 most naturally means the morning class or morning classes.

Korean nouns often do not show singular vs. plural clearly, so 수업 can sometimes feel a little flexible in English:

• 오전 수업이 끝나고 나서 = after the morning class ends
• or sometimes after morning classes are over

The particle 이/가 marks the subject of the verb.

Here, the verb is 끝나다 (to end / to be over), so 수업이 means the class is the thing that ends.

So the structure is:

• 오전 수업이 끝나다 = the morning class ends

If you used 을/를 here, it would sound like the class is a direct object, which does not fit 끝나다.

The dictionary form is 끝나다, which means to end, to be over, or to finish in an intransitive sense.

In the sentence:

• 끝나고 나서 = after ending / after it ends

This is made from:

• 끝나- (verb stem)
• -고 나서 = after doing

So:

• 오전 수업이 끝나고 나서 = after the morning class ends

-고 나서 specifically emphasizes after doing X, then Y happens.

So:

• 끝나고 나서 점심을 먹어요 = after class ends, I eat lunch

Other options are possible, but they feel slightly different:

• 끝나고 점심을 먹어요
  Very natural. It means class ends, and then I eat lunch. Slightly simpler and less emphatic.

• 끝나서 점심을 먹어요
  This can sometimes sound more like because it ended, I eat lunch or be more context-dependent. It is less clear for beginners.

So -고 나서 is often the safest way to say after.

This is a very common question.

• 끝나다 = to end / to be over
  This is intransitive, so the thing ends by itself.
• 끝내다 = to finish / to end something
  This is transitive, so someone actively finishes something.

In this sentence, the class is what ends:

• 수업이 끝나요 = the class ends

If you said:

• 수업을 끝내요

that would mean someone finishes the class or brings the class to an end. That can work in some situations, but it is a different structure.

Because 점심 is the object of 먹어요 (eat).

• 점심을 먹어요 = eat lunch

Here:

• 점심 = lunch
• 을/를 = object marker
• 먹어요 = eat

In casual speech, Korean often drops object particles when the meaning is obvious:

• 점심 먹어요 = I eat lunch

That is also very natural.
Using 점심을 just sounds a little more complete or explicit.

Korean often leaves out the subject when it is clear from context.

So even though English usually needs I, Korean does not always say it.

This sentence could mean:

• I eat lunch after the morning class ends
• We eat lunch after the morning class ends
• in some contexts, even he/she eats lunch...

If you want to make I explicit, you can say:

• 저는 오전 수업이 끝나고 나서 점심을 먹어요.

But in normal conversation, leaving it out is very common.

Because Korean normally puts the main verb at the end.

A very rough Korean word order is:

• time / setting + subject + other information + verb

So this sentence is structured like:

• 오전 수업이 끝나고 나서 = after the morning class ends
• 점심을 = lunch
• 먹어요 = eat

That is why the full sentence naturally ends with 먹어요.

먹어요 is the polite everyday style, often called the 해요체 style.

It is very common in conversation and sounds polite without being stiff.

Compare:

• 먹어 = casual / plain speech
• 먹어요 = polite everyday speech
• 먹습니다 = formal, more official or stiff

So 먹어요 is a very useful standard form for learners.

It can mean either, depending on context, but without extra context it often sounds like a habit or routine:

• After morning class ends, I eat lunch.

Korean present tense is flexible. It can describe:

• habits
• general truths
• scheduled or near-future actions

So this sentence could also be used for something happening today, if the situation makes that clear.

If you wanted to make it clearly past, you would say:

• 오전 수업이 끝나고 나서 점심을 먹었어요.
  = I ate lunch after the morning class ended.

In careful spelling it is 끝나고 나서, but in actual pronunciation it sounds closer to:

• 끈나고 나서

This happens because the final consonant in 끝 changes in sound before ㄴ.
You do not need to change the spelling, but it is useful to recognize the pronunciation when listening.

So learners may hear something like:

• 오전 수업이 끈나고 나서 점심을 먹어요

even though it is written 끝나고 나서.