Avant que mes parents arrivent, je range ma chambre.

Avant que means before when it introduces a whole clause with its own subject and verb.

In this sentence:

• mes parents arrivent = a clause with subject + verb
• so French uses avant que

A useful contrast:

• Avant que mes parents arrivent... = Before my parents arrive...
• Avant d’arriver... = Before arriving...

So avant que is used because there is a separate subject: mes parents.

Because avant de is followed by an infinitive, not a conjugated verb.

Use avant de when the subject stays the same:

• Je range ma chambre avant de partir.
  I tidy my room before leaving.

Use avant que when there is a different subject in the second part:

• Je range ma chambre avant que mes parents arrivent.

Here, the subject changes:

• je range
• mes parents arrivent

That is why avant que is required.

Because avant que normally triggers the subjunctive in French.

French uses the subjunctive after certain expressions when the action is seen as:

• not yet completed
• uncertain from the speaker’s point of view
• dependent on another action

With avant que, the action in that clause has not happened yet at the moment being talked about, so French uses the subjunctive:

• avant que mes parents arrivent

This is one of those grammar patterns that learners usually memorize as a set phrase:

• avant que + subjunctive

Good question: in this form, arrivent looks exactly the same in the present indicative and the present subjunctive.

For arriver:

• Indicative: ils arrivent
• Subjunctive: qu’ils arrivent

So in this sentence, you know it is subjunctive because of the structure:

• avant que + subjunctive

With other subjects, the difference can be easier to notice. For example:

• avant que nous arrivions
• avant que vous arriviez

Those forms clearly show the subjunctive.

As written, je range ma chambre is in the present tense, so it most naturally sounds like a habit or a repeated action:

• I tidy my room before my parents arrive.

In other words, this can mean Whenever my parents are about to arrive, I tidy my room first.

If you want to talk about one specific future event, French would more often use a future or near-future form in the main clause:

• Je rangerai ma chambre avant que mes parents arrivent.
• Je vais ranger ma chambre avant que mes parents arrivent.

Notice that even if the main clause becomes future, after avant que French still uses the subjunctive, not the future.

Because after avant que, French does not use the future tense. It uses the subjunctive.

So French says:

• avant que mes parents arrivent

not:

• avant que mes parents arriveront

This is an important difference from what learners might expect. The time reference may be future, but the grammar after avant que is still:

• avant que + subjunctive

Yes. That is completely correct.

French can place the avant que clause either:

• before the main clause: Avant que mes parents arrivent, je range ma chambre.
• after the main clause: Je range ma chambre avant que mes parents arrivent.

The meaning stays the same. Putting the avant que clause first gives it a little more emphasis.

Also, when the subordinate clause comes first, the comma is natural and common:

• Avant que mes parents arrivent, je range ma chambre.

You may indeed see:

• Avant que mes parents n’arrivent, je range ma chambre.

That ne is called an expletive ne. It does not make the sentence negative.

So this does not mean:

• before my parents do not arrive

It simply appears in certain formal or careful styles after expressions like avant que, à moins que, de peur que, etc.

In modern spoken French, people very often leave it out, as in your sentence:

• Avant que mes parents arrivent...

So both are possible, but the version without ne is very common in everyday speech.

Ranger usually means to put in order, to tidy up, or to put away.

So:

• ranger ma chambre = tidy my room

It usually suggests organizing the room, putting things back in place, and making it neat.

It is not exactly the same as deep cleaning. For example:

• ranger sa chambre = tidy one’s room
• nettoyer sa chambre = clean one’s room

In everyday English, though, clean my room is sometimes used loosely for both ideas.

Yes.

• mes = my for plural nouns
• parents = parents

So:

• mon père = my father
• ma mère = my mother
• mes parents = my parents

Because parents is plural, French uses mes, not mon or ma.

If the same person is doing both actions, French often switches from avant que to avant de + infinitive.

For example:

• Avant de ranger ma chambre, je prends un café.
• Je range ma chambre avant de sortir.

Here, the subject of both actions is the same person, so French does not need a full clause with que.

Compare:

• Avant que mes parents arrivent, je range ma chambre.
  different subjects: mes parents / je

• Avant d’arriver, je téléphone.
  same subject for both actions

That difference is one of the most important things to notice in this sentence.