jawonbongsajaga mulpumeul seuseuro bunryuhaesseoyo.

-가 is the subject marker. It marks 자원봉사자 as the doer of the action.

In this sentence, 자원봉사자가 sounds like a neutral statement about who did the sorting.
If you used -는 instead, the sentence would sound more like you are introducing or contrasting the volunteer as the topic:

• 자원봉사자가 물품을 스스로 분류했어요.
  = It was the volunteer who sorted the items / A volunteer sorted the items.

• 자원봉사자는 물품을 스스로 분류했어요.
  = As for the volunteer, they sorted the items themselves.

Both can be grammatical, but -가 is very natural for a simple standalone sentence like this.

-을 / -를 is the object marker. It marks the thing that receives the action of the verb.

So in:

• 물품을 = the items / supplies as the thing being sorted

The volunteer is doing the action, and the items are what gets sorted.

A quick breakdown:

• 자원봉사자가 = the volunteer (subject)
• 물품을 = the items/supplies (object)
• 분류했어요 = sorted / classified

물품 means something like items, goods, or supplies. It often sounds a bit more formal or administrative than everyday English thing.

Compare:

• 물품: formal, institutional, inventory-like
  
  • supplies, goods, items
• 물건: more everyday
  
  • thing, object, item

So if this sentence is about volunteering, donation sorting, warehouse work, aid supplies, etc., 물품 fits very well.

For example:

• 물품을 분류하다 = to sort supplies/items
• 물건을 정리하다 = to organize things/stuff

스스로 means by oneself, on one’s own, or of one’s own accord.

In this sentence, it suggests that the volunteer sorted the items personally or without relying on someone else to do it. Depending on context, it can carry one or both of these nuances:

• without help / independently
• voluntarily / on one’s own initiative

So 스스로 is not exactly the same as English myself/himself/herself, even though it can overlap in meaning. It is an adverb, so it modifies the verb 분류했어요.

Not exactly, though they can sometimes be similar.

• 스스로 = by oneself, on one’s own, of one’s own accord
• 직접 = directly, in person, personally

Compare the feeling:

• 스스로 분류했어요
  = sorted them on their own / by themselves

• 직접 분류했어요
  = sorted them personally, rather than having someone else do it

In many contexts, both are possible, but 스스로 emphasizes independence or self-initiation, while 직접 emphasizes personal involvement.

분류했어요 comes from the dictionary form 분류하다, which means to classify or to sort.

It breaks down like this:

• 분류하다 = to classify / sort
• 분류해요 = classify / sort (present polite)
• 분류했어요 = classified / sorted (past polite)

Why 했어요?
Because 분류하다 is a 하다 verb:

• 하다 → 해요 (present)
• 하다 → 했어요 (past)

So:

• 분류하다 → 분류해요 → 분류했어요

The ending -어요 makes the sentence polite and conversational.

It is in the polite informal style (often called 해요-style).

That means it is polite enough for everyday conversation, speaking to strangers, coworkers, teachers, customers, and so on, but it is not the most formal style.

Compare:

• 분류했어요 = polite everyday speech
• 분류했습니다 = formal polite speech
• 분류했어 = casual speech

So this sentence sounds natural in normal polite conversation.

Yes, 스스로 can move around somewhat because Korean word order is flexible, especially with adverbs.

The most neutral order here is:

• 자원봉사자가 물품을 스스로 분류했어요.

But you could also hear:

• 자원봉사자가 스스로 물품을 분류했어요.
• 물품을 자원봉사자가 스스로 분류했어요.

All of these are possible, though the nuance or emphasis may shift slightly.

A useful rule:

• Korean usually places the verb at the end
• Adverbs like 스스로 often appear before the verb
• Subject and object can move more freely because particles show their roles

It is natural, but some of the vocabulary is a little on the formal/organized-task side.

In particular:

• 물품 is more formal than 물건
• 분류하다 sounds a bit systematic or task-oriented, like sorting inventory, donations, documents, or supplies

So this sentence fits very well in contexts like:

• volunteer work
• donation centers
• warehouses
• event preparation
• relief supplies

In very casual everyday speech, a speaker might choose simpler words depending on context, but this sentence itself is perfectly normal.

By itself, 자원봉사자 does not show gender, and Korean nouns usually do not have to mark singular vs. plural the way English does.

So depending on context, it could refer to:

• a volunteer
• the volunteer
• sometimes even volunteers, if context makes that clear

If the speaker wanted to make plural more explicit, they could say:

• 자원봉사자들이

But Korean often leaves number unstated unless it matters.

So this sentence does not tell you:

• whether the volunteer is male or female
• whether it is definitely singular unless context makes that clear

Korean usually does not use articles like a or the, and it often leaves possessive words unstated when the meaning is obvious from context.

So English might need to choose:

• A volunteer sorted the items on their own.
• The volunteer sorted the supplies by themselves.

But Korean can simply say:

• 자원봉사자가 물품을 스스로 분류했어요.

This is very normal. Korean often lets context do work that English does with articles and pronouns.