kono sekken ha ii nioi ga simasu.

You’re right: normal Japanese is usually written without spaces.

So the standard writing would be:

この石けんはいい匂いがします。

The spaces here are just for learners, to make it easier to see the words and particles:

• この
• 石けん
• は
• いい
• 匂い
• が
• します

この must be followed by a noun, while これ stands alone.

• この石けん = this soap
• これ = this one / this

So in this sentence, because soap is stated explicitly, you use この:

• この石けん = this soap

If you wanted to use これ, you would need to remove 石けん:

• これはいい匂いがします。 = This has a nice smell.

They do different jobs.

• は marks the topic: what the sentence is about
• が marks the subject of the smaller phrase before the verb

In this sentence:

• この石けんは = as for this soap...
• いい匂いがします = a nice smell occurs / it smells nice

So the sentence is structured like:

• Topic: this soap
• What about it? It gives off a nice smell

This pattern is very common in Japanese:

• A は B が します
• As for A, B is perceived / occurs

Literally, 匂いがする means something like:

• a smell occurs
• there is a smell
• it smells

So:

• いい匂いがします = it gives off a nice smell / it smells nice

Here, する is not the usual to do in the sense of performing an action yourself. In expressions like this, it means something more like to be sensed or to give off.

Common similar patterns are:

• 音がする = to make a sound
• 声がする = to hear a voice
• 味がする = to taste like...
• 匂いがする = to smell like...

いい and よい both mean good.

In modern Japanese, いい is much more common in everyday speech. So いい匂い is the normal, natural phrase for a nice smell.

You may still see よい in:

• more formal writing
• set expressions
• certain conjugated forms

For example:

• dictionary-style adjective: よい
• common everyday form before a noun: いい匂い
• past: よかった

So いい匂い is exactly what you should expect here.

Not necessarily.

匂い just means smell or odor in a general sense. Whether it is pleasant or unpleasant depends on context.

• いい匂い = a nice smell
• 変な匂い = a strange smell
• いやな匂い = an unpleasant smell

Also, Japanese has a nuance difference:

• 匂い often feels a bit more neutral or sometimes pleasant
• 臭い is more often used for a bad smell or stink

So in this sentence, the adjective いい tells you clearly that it is a pleasant smell.

Yes, it can be written in kanji as 石鹸.

However, in modern Japanese, this word is very often written in kana:

• せっけん
• 石けん
• sometimes 石鹸

Kana is common because:

• the kanji 鹸 is not very common
• kana is easier to read
• many everyday product words are often written partly or fully in kana

So 石けん is a very normal spelling.

します is the polite -masu form of する.

So:

• いい匂いがします = polite
• いい匂いがする = plain/casual

That means the casual version of the full sentence is:

この石けんはいい匂いがする。

You would use:

• します in polite conversation, class, customer situations, etc.
• する with friends, family, casual speech, or plain written style

Yes. That is also natural.

• この石けんはいい匂いです。
• この石けんはいい匂いがします。

Both can mean roughly This soap smells nice.

The nuance is slightly different:

• いい匂いです describes the soap as being a nice smell / having a nice scent
• いい匂いがします focuses a bit more on the smell as something you perceive

In many situations, the difference is small, and both are fine.

The basic order here is the natural one:

この石けんは いい匂いが します。

Japanese is more flexible than English, but particles show the role of each part, so the particles matter more than the exact position.

Still, not every rearrangement sounds equally natural. For learners, the safest pattern is:

• [topic] は [smell/taste/sound] が します

Examples:

• この花はいい匂いがします。
• このスープは変な味がします。
• 外で音がします。

So yes, Japanese has some flexibility, but this sentence is already in a very standard order.

A helpful breakdown is:

• この = this
• 石けん = soap
• は = topic marker
• いい = good / nice
• 匂い = smell
• が = subject marker
• します = does / occurs / is perceived

So the structure is:

• As for this soap, a nice smell occurs.

That literal meaning becomes natural English as:

• This soap smells nice.
• This soap has a nice smell.

This is a good example of how Japanese often expresses sensory ideas indirectly, using patterns like 音がする, 味がする, and 匂いがする.