kyou no hirugohan ha eki de katta pan ni simasu.

No. Standard Japanese is normally written without spaces:

今日の昼ご飯は駅で買ったパンにします。

Spaces are often added in textbooks or learning materials to make the parts easier to see.

今日の昼ご飯 means today’s lunch or lunch for today.

Here, の connects 今日 and 昼ご飯. It works a bit like ’s or of in English:

• 今日 = today
• 昼ご飯 = lunch
• 今日の昼ご飯 = today’s lunch

So の is linking the time word to the noun it describes.

は marks the topic of the sentence.

So:

• 今日の昼ご飯は = As for today’s lunch, ...

The speaker is setting up today’s lunch as the thing they are talking about. This does not mean 昼ご飯 is the subject in exactly the same way as English grammar; は is a topic marker, not just a subject marker.

Because で marks the place where an action happens.

• 駅で買った = bought at the station

The action is 買った = bought, and that action happened at the station, so で is the natural particle.

By contrast, に is often used for:

• destination: 駅に行く = go to the station
• time: 3時に行く = go at 3 o’clock
• existence with ある / いる, etc.

So 駅で is correct because buying is an action performed there.

This is a very common Japanese structure: a clause comes before the noun and directly modifies it.

• 駅で買ったパン = the bread (that I) bought at the station

In English, we often need words like that, which, or I bought after the noun. Japanese does it the other way around:

• 駅で買った = bought at the station
• パン = bread

So literally it is something like:

• station-at bought bread

Japanese does not need a relative pronoun like that here.

Because 買った is describing when the bread was bought, not when it will be eaten.

The bread is being identified as:

• the bread that was bought at the station

So the buying happened in the past, even if the eating or choosing is happening now.

This is normal in Japanese relative clauses.

Here, N にします is a set pattern meaning:

• decide on N
• choose N
• go with N

So:

• パンにします = I’ll have bread / I’ll go with bread / I’ll choose bread

It does not mean make something into bread here.

This use of にする is very common when choosing food, drinks, or options:

• コーヒーにします = I’ll have coffee
• これにします = I’ll take this / I’ll choose this

Because this is not the pattern パンをする. The expression is N にする, not N をする.

In this pattern, に marks the thing you decide on:

• パンにする = choose bread
• これにする = choose this

So に is required by the expression itself.

Yes, the subject is omitted, which is very common in Japanese.

In 駅で買ったパン, the understood meaning is usually:

• the bread I bought at the station

But Japanese often leaves out I, you, we, etc. when the context makes it clear.

So the sentence naturally implies the speaker is talking about bread they bought, unless context suggests someone else.

A natural translation would be something like:

• For today’s lunch, I’ll have the bread I bought at the station.
• I think I’ll make the bread I bought at the station my lunch today.
• As for lunch today, I’ll go with the bread I bought at the station.

The nuance of にします is a decision or choice, so it sounds a bit like the speaker is deciding what to eat.

They mean different things.

• パンです = It is bread
  This only identifies what it is. It does not express a decision.

• パンを食べます = I will eat bread
  This directly states the action of eating.

• パンにします = I’ll go with bread / I’ll choose bread
  This focuses on the speaker’s choice.

So にします is especially natural when someone is deciding what to have for a meal.