piryohan mulpumeun haengsajang ane isseoyo.

In Korean, words that describe a noun usually come before the noun.

So 필요한 물품 literally means needed items or necessary supplies.

• 필요한 = needed / necessary
• 물품 = items / supplies

This is different from English, where a full phrase like that are needed comes after the noun:

• Korean: 필요한 물품
• English: the items that are needed

필요하다 is the dictionary form, meaning to be necessary.

To modify a noun, Korean changes it into a noun-modifying form:

• 필요하다 → 필요한

So:

• 필요한 물품 = items that are necessary
• literally, necessary items

This is a very common pattern in Korean:

• 중요하다 → 중요한 = important
• 편리하다 → 편리한 = convenient
• 필요하다 → 필요한 = necessary / needed

물품 means items, goods, supplies, and it often sounds a bit more formal or official.

By contrast, 물건 is a more everyday word meaning thing, object, item.

So in a notice, announcement, or event-related sentence, 물품 sounds natural because it fits a more formal context.

For example:

• 물건 = everyday item / thing
• 물품 = supplies / articles / goods

In this sentence, 물품 suggests something like event supplies, required items, or necessary materials.

은 is the topic particle.

So 물품은 means something like:

• as for the necessary items
• the necessary items, ...

This often gives a nuance of setting the topic and then saying something about it.

So the sentence structure is roughly:

• 필요한 물품은 = as for the necessary items
• 행사장 안에 있어요 = they are inside the event venue

Using 은 can sound natural when:

• the speaker is talking about a known topic
• the sentence answers a question like Where are the necessary supplies?
• there may be some mild contrast, such as the necessary items are inside (not somewhere else)

Yes, 필요한 물품이 행사장 안에 있어요 is grammatically correct.

The difference is mainly nuance:

• 물품은: sets the necessary items as the topic
  
  • As for the necessary items, they are inside the venue.
• 물품이: more neutral subject marking
  
  • The necessary items are inside the venue.

In many situations, 은 sounds more natural if the speaker is talking about something already being discussed.

It means inside the event venue or in the event hall/site.

Breakdown:

• 행사장 = event venue / event site / event hall
• 안 = inside
• 에 = location particle

So:

• 행사장 안에 = inside the event venue

Here, 안 is functioning like a noun meaning the inside, so it takes the particle 에.

에 is used to mark the location where something exists or is located when the verb is 있다.

Since 있어요 means is/are there or exists/is located, the place before it is marked with 에:

• 행사장 안에 있어요 = it is inside the event venue

This is a very common pattern:

• 책상 위에 있어요 = it is on the desk
• 가방 안에 있어요 = it is inside the bag
• 교실에 있어요 = it is in the classroom

Here, 있어요 means is/are located, is there, or exists.

It comes from 있다, which can mean:

• to exist / to be present
• to have

In this sentence, because there is a location phrase (행사장 안에), it clearly means to be located:

• 행사장 안에 있어요 = it is inside the venue / they are inside the venue

So this is not a possession meaning like I have something. It is a location/existence meaning.

Korean often does not explicitly mark plural when the meaning is already clear from context.

So 물품 can naturally mean:

• item
• items
• supplies

Even though English often requires a choice between singular and plural, Korean frequently leaves that unstated unless it is important.

You could sometimes see 물품들, but in a sentence like this, just 물품 is more natural.

Yes, compared with English, Korean word order is different.

The sentence is organized like this:

• 필요한 물품은 = the necessary items
• 행사장 안에 = inside the event venue
• 있어요 = are / are located

So Korean puts the verb at the end:

• The necessary items / inside the event venue / are

That final-verb pattern is one of the most important differences between Korean and English.