Pour que le dîner soit prêt à l'heure, Paul commence à cuisiner pendant que Marie se connecte à la visioconférence.

Pour que means so that / in order that and it must be followed by a conjugated verb.

• Pour que le dîner soit prêt... = So that dinner is ready...
• If you use pour by itself, it is normally followed by an infinitive, not a full clause with its own subject.

Compare:

• Paul cuisine pour être prêt à l'heure. = Paul cooks in order to be ready on time.
• Paul cuisine pour que le dîner soit prêt à l'heure. = Paul cooks so that the dinner is ready on time.

In your sentence, the subject of the second verb is le dîner, so French uses pour que.

Because pour que triggers the subjunctive in French.

So:

• le dîner est prêt = the dinner is ready
• pour que le dîner soit prêt = so that the dinner may be ready / so that the dinner is ready

After expressions of purpose, desire, necessity, doubt, emotion, and similar ideas, French often uses the subjunctive. Pour que is one of the most common triggers.

So soit is the correct form here, not est.

Soit is the present subjunctive form of the verb être for il / elle / on.

The present subjunctive of être is:

• que je sois
• que tu sois
• qu'il / elle / on soit
• que nous soyons
• que vous soyez
• qu'ils / elles soient

Since le dîner is singular, French uses qu'il soit type agreement, so you get:

• pour que le dîner soit prêt

Prêt is an adjective, and it agrees with the noun it describes: le dîner.

Since dîner is:

• masculine
• singular

the adjective must also be:

• masculine singular → prêt

If the noun were feminine, you would get prête:

• pour que la soupe soit prête

If plural:

• pour que les plats soient prêts

Because commencer is commonly followed by à + infinitive when it means to start doing something.

So:

• commencer à cuisiner = to start cooking
• commencer à lire = to start reading
• commencer à parler = to start speaking

French learners often want to say commence cuisiner, but that is not correct here. The normal pattern is:

• commencer à + infinitive

You may also see commencer par + infinitive, but that means to begin by doing something, which is slightly different.

Because pendant que is used before a clause with a conjugated verb, while pendant by itself is usually used before a noun or a time expression.

In your sentence:

• pendant que Marie se connecte...

This works because Marie se connecte is a full clause.

Compare:

• pendant la réunion = during the meeting
• pendant une heure = for an hour
• pendant que Marie se connecte = while Marie is connecting / while Marie logs in

So if there is a subject + verb after it, pendant que is the right choice.

Because the verb is commonly se connecter à, meaning to log in to / connect to something.

So:

• Marie se connecte à la visioconférence = Marie logs in to the video conference

This is a pronominal/reflexive verb in French. Even though English just says connect or log in, French usually says se connecter.

Examples:

• Je me connecte au site. = I log in to the website.
• Nous nous connectons au réseau. = We connect to the network.

So the se is part of the normal verb pattern.

Because se connecter normally takes the preposition à.

So the pattern is:

• se connecter à + noun

Examples:

• se connecter à Internet
• se connecter au réseau
• se connecter à la plateforme
• se connecter à la visioconférence

Here, visioconférence is feminine singular, so:

• à + la visioconférence → à la visioconférence

If the noun were masculine singular, you would often get au:

• se connecter au serveur

French often uses the simple present where English uses either:

• the simple present, or
• the present progressive (is ...-ing)

So:

• Paul commence à cuisiner can mean Paul starts cooking or Paul is starting to cook
• Marie se connecte à la visioconférence can mean Marie logs in or Marie is logging in / connecting

French does have ways to emphasize an action in progress, such as être en train de, but it is not necessary here.

So the simple present is completely natural.

Here à l'heure means on time or at the right time.

So:

• prêt à l'heure = ready on time

This expression is very common:

• arriver à l'heure = to arrive on time
• être à l'heure = to be on time

In your sentence, it means the dinner should be ready when it is supposed to be, not late.

The comma separates the introductory subordinate clause from the main clause.

Structure:

• Pour que le dîner soit prêt à l'heure, = introductory purpose clause
• Paul commence à cuisiner... = main clause

This is very similar to English punctuation:

• So that dinner is ready on time, Paul starts cooking...

The comma helps readability. In French, when a subordinate clause comes first, using a comma is very normal.

Yes. Afin que also means so that / in order that, and it also requires the subjunctive.

So you could say:

• Afin que le dîner soit prêt à l'heure, Paul commence à cuisiner...

This is correct and a little more formal or written in tone than pour que. In everyday speech, pour que is often more common.

Yes, visioconférence is a correct and standard French word meaning videoconference or video call/conference, depending on context.

That said, in everyday speech, many speakers also use shorter or more modern expressions such as:

• une visio
• une réunion en visio
• un appel vidéo

But se connecter à la visioconférence is perfectly understandable and grammatically correct.