أولئك طلاب.

In Arabic, a simple present-tense sentence like Those are students often has no written or spoken word for are.

So:

• أولئك = those
• طلاب = students

Together, أولئك طلاب naturally means Those are students.

This kind of sentence is called a nominal sentence. In grammar terms:

• أولئك is the subject
• طلاب is the predicate

If you wanted a past or future meaning, Arabic would usually use a verb, for example:

• كانوا طلابًا = They were students
• سيكونون طلابًا = They will be students

أولئك is a demonstrative word meaning those.

It is used for a plural group that is farther away or being treated as distant in some way.

A basic contrast is:

• هؤلاء = these
• أولئك = those

So:

• هؤلاء طلاب = These are students
• أولئك طلاب = Those are students

In beginner Arabic, you will most often meet أولئك when referring to people.

It is usually pronounced ulāʾika.

A rough English-style guide is:

• u-LAA-i-ka

Notes:

• the LAA part is long
• there is a small glottal stop before the i sound
• the final -ka is part of the word

A more careful pronunciation is:

• u-laa-ʾi-ka

Because here طلاب is being used as an indefinite predicate: students, not the students.

So the sentence means:

• Those are students

not:

• Those are the students
• Those students

This is a very common Arabic pattern:

• demonstrative + indefinite noun

to mean something like That/Those is/are a ... / ...s

For example:

• هذا بيت = This is a house
• هؤلاء معلمون = These are teachers
• أولئك طلاب = Those are students

This is an important difference.

• أولئك طلاب = Those are students
  
  • a complete sentence
• أولئك الطلاب = those students
  
  • a noun phrase, not a full sentence by itself

So the presence or absence of ال changes the structure:

• طلاب without ال = predicate students
• الطلاب with ال = noun the students

If you want to say Those are the students, Arabic often says:

• أولئك هم الطلاب

That extra هم helps make it clearly a full sentence.

For plural demonstratives, أولئك does not usually change for gender.

That means you can use أولئك with:

• a group of males
• a group of females
• a mixed group

The gender is usually shown by the noun that comes after it.

Examples:

• أولئك طلاب = Those are students (male or mixed group)
• أولئك طالبات = Those are female students

So أولئك stays the same, while the noun changes if needed.

طلاب is the plural of طالب, which means student.

So:

• طالب = student (masculine singular)
• طلاب = students (masculine plural, often also used for mixed groups)

This is a broken plural, which means Arabic does not just add a simple ending; the internal pattern of the word changes.

Related forms:

• طالب = one male student
• طالبة = one female student
• طلاب = male students / mixed students
• طالبات = female students

So in أولئك طلاب, the noun tells you that the group is male or mixed, not exclusively female.

Yes—if the sentence is fully vowelled, there would be a case ending.

The fully vocalized form is:

• أُولَٰئِكَ طُلَّابٌ

Here:

• طلابٌ ends in ـٌ because it is nominative
• that nominative ending fits its role as the predicate in this nominal sentence

But in normal everyday Arabic writing, short vowels and tanwīn are usually not written, so you simply see:

• أولئك طلاب

Also, أولئك itself is an indeclinable word, so its form does not change for case the way many nouns do.

Yes, you could.

• هم طلاب = They are students
• أولئك طلاب = Those are students

The difference is:

• هم is a personal pronoun: they
• أولئك is a demonstrative: those

So use:

• هم when you are referring back to people already mentioned
• أولئك when you are pointing them out as those people

Both are grammatically fine, but they do not feel exactly the same.

Because in this sentence أولئك is the subject of the nominal sentence.

Arabic commonly builds this kind of sentence as:

• demonstrative + predicate

So:

• أولئك طلاب = Those are students

If you want a phrase like those students, Arabic still normally puts the demonstrative first:

• أولئك الطلاب = those students

So in both the sentence and the noun phrase, the demonstrative naturally comes before the noun here.