keopie seoltangeul jogeum neoheo juseyo.

Here, 에 marks the place or target that something is going into. So 커피에 means in the coffee or into the coffee.

In this sentence:

• 커피에 = into the coffee
• 설탕을 = sugar
• 넣어 주세요 = please put/add

So 에 is not marking the direct object. It is marking the destination/location where the sugar is added.

을/를 is the direct object particle in Korean. It marks the thing being directly acted on by the verb.

Here, the verb is 넣다 = to put in / to add, and the thing being added is 설탕, so:

• 설탕을 = sugar + object marker

A native English speaker might expect coffee to be the object, but in Korean the object is the thing being put in, while the container or destination is marked with 에.

조금 means a little or a small amount.

In this sentence, it tells you how much sugar to add, so it modifies the action 넣어 주세요.

You can think of it as:

• 설탕을 조금 넣어 주세요 = please add sugar in a small amount

It comes before the verb phrase, which is normal in Korean.

Yes. In everyday speech, 좀 is very common.

So you can say:

• 커피에 설탕을 좀 넣어 주세요.

This sounds natural and conversational.
The difference is roughly:

• 조금 = a little, slightly more explicit/literal
• 좀 = shortened, very common in speech, sometimes softer in tone

In many situations, 좀 sounds even more natural.

The dictionary form is 넣다, which means to put in, to insert, or to add.

The form breaks down like this:

• 넣다 = dictionary form
• 넣어 = connective/polite request stem
• 주세요 = please give

Together, 넣어 주세요 literally means something like please do the action of putting it in for me/us, but in natural English it just means please add/put in.

Both can be polite, but they feel a little different.

• 넣어 주세요 = please add it
• 넣으세요 = add it / please add it

For requests to someone, -아/어 주세요 often sounds warmer and more like a direct request for help or service. That is why it is very common in restaurants, cafes, and everyday polite speech.

So in this kind of situation, 넣어 주세요 is very natural.

Yes, in this construction it is normally written separately:

• 넣어 주세요

This is because 주다 is functioning as an auxiliary verb meaning something like do for me/us.

In casual writing, some people may write it together, but standard spacing is:

• 넣어 주세요

The same pattern appears in many requests:

• 봐 주세요 = please look
• 도와 주세요 = please help
• 기다려 주세요 = please wait

Korean usually puts the verb at the end of the sentence. That is one of the biggest differences from English.

This sentence is structured like:

• 커피에 = into the coffee
• 설탕을 = sugar
• 조금 = a little
• 넣어 주세요 = please add

So Korean often builds the sentence first with particles and details, then finishes with the verb.

A very literal order would be:

• Into the coffee sugar a little add please

That sounds strange in English, but it is normal in Korean.

Yes, in everyday conversation, Korean often drops 을/를 when the meaning is still clear.

So both are possible:

• 커피에 설탕을 조금 넣어 주세요.
• 커피에 설탕 조금 넣어 주세요.

The version with 을 is a little more complete and clear grammatically.
The version without it sounds natural in casual spoken Korean too.

커피에 설탕을 조금 넣어 주세요 is polite and appropriate in many everyday situations.

It uses 주세요, which is a standard polite request form. It is suitable for:

• speaking to staff
• making a polite request
• speaking to someone you do not know well

It is not extremely formal, but it is respectful and very natural.

If you wanted to sound more formal, you could say:

• 커피에 설탕을 조금 넣어 주세요 = polite everyday
• 커피에 설탕을 조금 넣어 주십시오 = more formal

In this sentence, it is best understood as in the coffee or into the coffee.

The particle 에 can have several meanings depending on the verb, including:

• at
• in
• to
• on

With 넣다 (to put in), it marks the place something is inserted into, so 커피에 means the coffee is the thing receiving the sugar.

So the sense is:

• put sugar into the coffee