chinguga mollae seonmureul junbihaessseupnida.

가 marks 친구 as the subject of the sentence.

• 친구가 = the friend is the one doing the action
• 친구는 would sound more like as for the friend..., often with contrast or topic emphasis

In this sentence, 친구가 simply introduces the friend as the person who secretly prepared the gift. It sounds natural when presenting new information.

몰래 is an adverb, so it describes how the action was done.

Here it means something like:

• secretly
• without anyone knowing
• on the sly

So 몰래 준비했습니다 means the gift was prepared secretly.

In Korean, adverbs usually come before the verb or before the part of the sentence they modify.

So:

• 몰래 선물을 준비했습니다

means the action of preparing the gift was done secretly.

Korean word order is flexible, but putting 몰래 before the object and verb is very natural.

For example, these can also work depending on emphasis:

• 친구가 선물을 몰래 준비했습니다.
• 몰래 친구가 선물을 준비했습니다.

But the original sentence is the most neutral and natural.

을/를 marks the direct object, the thing receiving the action.

• 선물 = gift
• 선물을 = the gift

Since 준비하다 means to prepare, the thing being prepared is the object, so 선물을 is used.

Because 선물 ends in a consonant, it takes 을, not 를.

The dictionary form is 준비하다.

This verb is made from:

• 준비 = preparation
• 하다 = to do

So literally, it is like to do preparation, but in natural English it means to prepare.

The form 준비했습니다 breaks down like this:

• 준비하- = verb stem
• -였- / -았- / -했- = past tense part
• -습니다 = formal polite ending

So 준비했습니다 means prepared in a formal polite style.

Yes. -했습니다 is a past-tense form, so it shows the preparing happened in the past.

It usually suggests the action was completed:

• the friend prepared the gift
• the preparation has already been done

Korean past tense often covers what English expresses as simple past, and sometimes it can also feel close to present perfect depending on context.

Not exactly. -습니다 is a formal polite sentence ending, not a subject honorific.

That means it shows politeness toward the listener, not respect toward the subject.

So in this sentence:

• 준비했습니다 = formal polite
• it does not mean the friend is being specially honored

If you wanted to honor the subject, you would use something like 준비하셨습니다 instead, but that would only be appropriate if the subject deserves that respect.

Yes. Korean nouns usually do not change form for singular vs. plural.

So 친구 can mean:

• friend
• friends

The sentence could mean one friend or multiple friends depending on context. If you want to make it clearly plural, you can say 친구들이, but Korean often leaves it unspecified unless needed.

No. 친구 is gender-neutral.

By itself, it does not tell you:

• whether the friend is male or female
• whether the friend is older or younger than the speaker

That information would need to come from context or other words.

Yes. Very often, Korean leaves out subjects when they are already understood from context.

So you could say:

• 몰래 선물을 준비했습니다.

and if everyone already knows who did it, that is completely natural.

Korean often omits:

• the subject
• the object
• other predictable information

The full sentence includes 친구가 because the speaker wants to state clearly that the friend is the one who prepared it.

Yes.

• 몰래 is common, everyday Korean
• 비밀리에 sounds more formal, written, or official

So 몰래 선물을 준비했습니다 sounds natural for ordinary conversation, especially for something personal like preparing a gift secretly.

If you used 비밀리에, it would sound much stiffer and less natural in this context.

Yes, 친구는 몰래 선물을 준비했습니다 is grammatically correct, but the nuance changes.

• 친구가 몰래 선물을 준비했습니다: neutral subject marking, often introducing who did it
• 친구는 몰래 선물을 준비했습니다: topic marking, possibly implying contrast such as the friend, at least, prepared the gift secretly

So both are possible, but 가 fits better if you are simply stating the event.

Korean is usually an SOV language:

• Subject + Object + Verb

English is usually SVO:

• Subject + Verb + Object

So in Korean:

• 친구가 = subject
• 선물을 = object
• 준비했습니다 = verb at the end

This is one of the most important sentence patterns in Korean. Adverbs like 몰래 usually appear before the final verb as well.