Άνοιξε λίγο το παράθυρο, μην γεμίσει το δωμάτιο μυρωδιά από το καθαριστικό.

Here Άνοιξε is the aorist imperative of ανοίγω, so it means Open and is addressed to one person.

That same form can also be the past tense he/she opened, so context has to tell you which one it is. In this sentence, it is clearly an instruction:

Άνοιξε λίγο το παράθυρο = Open the window a little.

The aorist imperative is normal here because the speaker wants one complete action: open it once. Greek often uses:

• aorist imperative for a single, whole action
• present imperative for repeated or ongoing action

So Άνοιξε fits better than Άνοιγε here.

Λίγο here means a little, slightly, or just a bit.

It modifies Άνοιξε, so:

• Άνοιξε λίγο το παράθυρο = Open the window a little

In this context, it most naturally means not all the way / just slightly.
Depending on context, λίγο can sometimes also mean for a short while, but here the most likely meaning is only a bit.

This is a very common Greek pattern after a command. It expresses something the speaker wants to prevent.

So:

• Άνοιξε λίγο το παράθυρο, μην γεμίσει το δωμάτιο...

means something like:

• Open the window a little, so the room doesn’t fill...
• Open the window a little, in case the room fills...
• Open the window a little, before the room fills...

In natural English, we often make this smoother than the Greek structure. The Greek is compact and very idiomatic.

Because δεν negates indicative statements, while μη(ν) is used with subjunctive, imperatives, and related non-indicative forms.

Compare:

• Δεν γεμίζει το δωμάτιο. = The room isn’t filling up.
  This is a statement.

• Μην γεμίσει το δωμάτιο. = So that the room doesn’t fill up / lest the room fill up.
  This is not a plain statement; it expresses something to avoid.

So in this sentence, μην is the correct negative particle.

Γεμίσει is the aorist subjunctive form, and that is what Greek normally uses after μην in this kind of clause.

The aorist here views the event as one whole thing:

• the room filling up with smell

The speaker wants to prevent that event from happening.

If you used γεμίζει, that would be indicative present, which does not fit after μην in this structure. A present subjunctive-type meaning would suggest something more ongoing or repeated, which is not the main idea here.

So μην γεμίσει is the natural choice for so that it doesn’t end up filling.

In this sentence, το δωμάτιο is best understood as the subject of γεμίσει:

• μην γεμίσει το δωμάτιο μυρωδιά...
• literally: so that the room doesn’t fill up with smell...

This may feel a little different from English, because English often says:

• so the smell doesn’t fill the room

But Greek can very naturally say it from the room’s point of view:

• the room fills up with smell

Also, το δωμάτιο is neuter singular, and its nominative and accusative forms are identical, so the form itself does not show you the role clearly. You understand it from the verb and the overall meaning.

This is a good question, because English learners often expect something more like with a smell or with the smell.

Here μυρωδιά is used in a fairly natural, somewhat compact way to mean smell / odor as the thing filling the room.

So:

• γεμίσει το δωμάτιο μυρωδιά
  means roughly
• the room fills with smell

About the two details:

1. No article
Greek often leaves out the article when the noun is being used in a more general or indefinite sense. Here it is not a specific smell already identified so much as odor/smell in general.

2. No με
You will also hear the fuller version:

• να γεμίσει το δωμάτιο με μυρωδιά

That may look more transparent to an English speaker.
Without με, the sentence is a bit more compact and colloquial, but the meaning is still clear.

So both the missing article and the missing με make the phrase feel more idiomatic and concise.

Από here means from, indicating the source of the smell.

So:

• μυρωδιά από το καθαριστικό = smell from the cleaning product

Το καθαριστικό literally means the cleaner / the cleaning product. Depending on context, English might translate it as:

• the cleaner
• the cleaning liquid
• the detergent
• the cleaning product

The Greek article το can refer to the specific cleaner the speakers already know about, even if English might or might not use the in the same situation.

Yes. A more explicit version would be:

• Άνοιξε λίγο το παράθυρο, για να μην γεμίσει το δωμάτιο μυρωδιά από το καθαριστικό.

That means very clearly:

• Open the window a little so that the room doesn’t fill with smell from the cleaner.

The original version without για να is shorter and a bit more immediate. It sounds like the speaker is saying:

• Open the window a bit, so it doesn’t end up smelling of cleaner.

So the original is natural, but για να μην would also be perfectly understandable and a little more explicit for a learner.

A fairly literal understanding is:

• Open the window a little, so the room doesn’t fill with smell from the cleaner.

But in more natural English, you might think of it as:

• Open the window a little so the room doesn’t start smelling like cleaner.
• Open the window a bit so the room doesn’t get filled with the smell of the cleaner.
• Open the window a little, so the room won’t smell strongly of the cleaning product.

That helps show how Greek and English organize the idea slightly differently, even though the meaning is the same.