Quelques étudiants restent dans la salle après la séance.

Quelques means some in the sense of a few / several. It gives a more specific idea than des, which often just means some in a general plural sense.

• Quelques étudiants = a few students / some students
• Des étudiants = students / some students

So quelques suggests a limited number more clearly.

It is plural because quelques refers to more than one student. In French, plural nouns usually take -s in writing.

• singular: un étudiant
• plural: des étudiants

The -s is usually not pronounced, but it is still required in writing.

Because the subject is plural: quelques étudiants. French verbs change form depending on the subject.

The verb here is rester in the present tense:

• je reste
• tu restes
• il/elle reste
• nous restons
• vous restez
• ils/elles restent

Since quelques étudiants = they, French uses restent.

Here, rester means to stay or to remain.

So quelques étudiants restent means that some students stay behind or remain instead of leaving.

Depending on context, English might translate it as:

• Some students stay in the room
• A few students remain in the room

In French, nouns usually need an article. So salle normally appears with la, une, le, etc.

• la salle = the room
• une salle = a room

French generally does not drop the article the way English sometimes can.

So:

• dans la salle = in the room

Salle often means room, but it can also mean hall, classroom, or auditorium, depending on context.

For example:

• salle de classe = classroom
• salle de réunion = meeting room
• salle de cinéma = movie theater auditorium

In this sentence, la salle most naturally means the room or possibly the classroom / hall, depending on the situation.

That is a normal French word order. The basic structure is:

subject + verb + place + time

Here:

• Quelques étudiants = subject
• restent = verb
• dans la salle = place
• après la séance = time

French is fairly flexible, but this order sounds very natural.

Séance usually means session, showing, meeting, or class period, depending on context.

So après la séance could mean:

• after the session
• after the class
• after the screening
• after the meeting

It is a bit broader than a single English word, so the exact translation depends on what kind of event is being described.

Après is a preposition by itself, meaning after. It is followed directly by a noun phrase.

• après la séance = after the session
• après le cours = after the class
• après le déjeuner = after lunch

You do not add de before the noun here.

A careful approximate pronunciation is:

kel-kuh zay-tu-dyan rest dahn la sal ah-prey la say-ahns

A few useful points:

• quelques sounds roughly like kelk
• étudiants has a nasal ending; the final -s is silent
• restent ends with a silent -ent
• dans has a nasal vowel
• salle sounds like sal
• après sounds like ah-prey
• séance is pronounced roughly say-ahns

Also notice the liaison in quelques étudiants: the s in quelques is pronounced like z before étudiants.

Yes, quite a lot.

Silent letters include:

• the final -s in étudiants
• the final -ent in restent
• the final -e in salle
• the final -e in séance is not pronounced as a separate sound

French spelling often shows grammar more clearly than pronunciation, so written endings are important even when they are silent.

Yes. The grammar would still work:

Des étudiants restent dans la salle après la séance.

That would mean something like Students remain in the room after the session or Some students stay in the room after the session.

The difference is mostly one of nuance:

• quelques étudiants = a few / several students
• des étudiants = some students / students in general

Yes. Restent is present tense. In French, the present tense can describe:

1. what is happening now
2. a general truth
3. a repeated or habitual action

So this sentence could mean either:

• Some students are staying in the room after the session
• Some students stay in the room after the session

The wider context tells you which meaning is intended.