saendeuwichie chijeureul neoheumyeon deo masisseoyo.

Because 에 marks the place or container that something goes into.

With 넣다 (to put in), a very common pattern is:

• A에 B를 넣다 = put B into A

So here:

• 샌드위치에 = into the sandwich
• 치즈를 = cheese as the thing being put in

If you translated the structure very literally, it would be something like put cheese into the sandwich.

Because 치즈 is the direct object of 넣다.

• 를/을 marks the thing that receives the action
• In this sentence, the action is 넣다 = to put in
• The thing being put in is 치즈

So:

• 치즈를 넣다 = to put in cheese

If you used 치즈가, the sentence structure would usually need a different verb, such as 들어가다:

• 치즈가 들어가면 더 맛있어요 = If cheese goes in / if the sandwich has cheese in it, it’s more delicious

That version is also natural, but it has a slightly different grammatical structure.

넣으면 comes from 넣다 (to put in) plus -으면, which often means if or when.

So:

• 넣다 = put in
• 넣으면 = if you put in / when you put in

In this sentence, 넣으면 connects the first idea to the result:

• 샌드위치에 치즈를 넣으면 = if/when you put cheese in a sandwich
• 더 맛있어요 = it’s more delicious

So the whole sentence means something like:

• If you put cheese in a sandwich, it’s more delicious.

It can mean either, depending on context.

In Korean, -으면 / -면 often covers both ideas:

• if
• when
• sometimes even a general whenever

Here, the sentence expresses a general truth or recommendation, so in natural English it is often understood as:

• If you put cheese in a sandwich, it’s more delicious
• or When you put cheese in a sandwich, it’s more delicious

English prefers if for this kind of general advice, but Korean -으면 itself is not limited to only one of those translations.

더 맛있어요 is the most natural way to say it’s more delicious / tastes better in this kind of sentence.

• 맛있어요 = is delicious / tastes good
• 더 맛있어요 = is more delicious / tastes better

Using 맛있어져요 would emphasize becoming delicious:

• 맛있어지다 = to become tasty

That can be grammatical, but here it sounds less natural than just saying the result directly. Korean often prefers the simpler predicate:

• 치즈를 넣으면 더 맛있어요 = If you add cheese, it tastes better

더 means more.

So:

• 맛있어요 = it’s delicious
• 더 맛있어요 = it’s more delicious / it tastes better

In natural English, 더 맛있어요 is often translated as tastes better, even though the literal meaning is more delicious.

The subject is not stated explicitly, and that is very normal in Korean.

From context, the implied meaning is something like:

• the sandwich is more delicious
• or a sandwich tastes better

Korean often leaves out subjects when they are obvious from the situation. So instead of saying something like:

• 샌드위치는 더 맛있어요

the speaker can simply say:

• 샌드위치에 치즈를 넣으면 더 맛있어요

The listener naturally understands what is meant.

Yes. 샌드위치 is a Korean loanword based on the English word sandwich.

Its pronunciation in Korean is approximately:

• saen-deu-wi-chi

A few things to notice:

• Korean often adds vowels to fit foreign words into Korean syllable structure.
• The English sand- becomes 샌드
• The ending becomes 위치

So even though it comes from English, its pronunciation follows Korean sound patterns.

Yes, you can, but the nuance changes.

• 샌드위치에 치즈를 넣으면 맛있어요 = If you put cheese in a sandwich, it’s delicious
• 샌드위치에 치즈를 넣으면 더 맛있어요 = If you put cheese in a sandwich, it’s more delicious / it tastes better

With 더, the sentence implies comparison:

• better than without cheese
• more delicious than before
• more delicious than another version

Without 더, it just says the sandwich is tasty with cheese, without explicitly comparing.

Often, yes, in this kind of context.

The basic meaning of 넣다 is to put in, insert, or place inside. But in food contexts, English often translates it more naturally as add.

So:

• 치즈를 넣다 literally = put in cheese
• natural English = add cheese

That means the sentence could be translated naturally as:

• If you add cheese to a sandwich, it tastes better.

Yes, that is also natural.

Compare the two:

• 샌드위치에 치즈를 넣으면 더 맛있어요

  • focuses on someone putting cheese in
  • uses 넣다 = to put in

• 샌드위치에 치즈가 들어가면 더 맛있어요

  • focuses more on cheese being in the sandwich
  • uses 들어가다 = to go in / be included

The difference is small in everyday conversation.

Very roughly:

• 넣으면 = if you put it in
• 들어가면 = if it’s in there / if it gets included

맛있어요 is the standard polite style, often called 해요체.

It is appropriate for:

• everyday conversation
• speaking politely with people you do not know well
• neutral, friendly situations

Related forms are:

• 맛있어 = casual
• 맛있어요 = polite
• 맛있습니다 = formal

So this sentence is polite but not stiff.

Because plain 에 is enough for the basic meaning: into the sandwich.

If you said 샌드위치에는, that would add contrast or emphasis, something like:

• As for sandwiches, if you put in cheese, they taste better
• or In sandwiches, cheese makes them taste better

So:

• 샌드위치에 = neutral, simple
• 샌드위치에는 = more contrastive or topic-like

The original sentence sounds natural and straightforward without that extra emphasis.