La professora els explica la resposta després de l'examen.

Here els means to them. It is an indirect object pronoun, so it marks the people who receive the explanation.

So the structure is:

• La professora = the teacher
• els = to them
• explica = explains
• la resposta = the answer

A very literal version would be: The teacher to-them explains the answer after the exam.

Because Catalan object pronouns usually go before a conjugated verb.

So Catalan says:

• els explica

not:

• explica els for this meaning

This is one of the biggest differences from English. English normally puts to them after the verb, but Catalan uses a short pronoun before it.

Yes. You could say:

• La professora explica la resposta als alumnes després de l'examen.

That means the same thing, with the receiver named explicitly: to the students.

In real Catalan, especially in speech, you may also hear both:

• La professora els explica la resposta als alumnes...

That is normal in many contexts, because Catalan often keeps the indirect object pronoun even when the full noun phrase is also present.

Explica is the third-person singular present of explicar.

It agrees with la professora, which is singular:

• la professora explica = the teacher explains

If the subject were plural, the verb would change:

• Les professores expliquen... = the teachers explain...

Catalan often drops subject pronouns when they are not needed.

So instead of saying:

• Ella explica la resposta

Catalan very often just says:

• Explica la resposta

In your sentence, the subject is already stated as la professora, so adding ella would usually be unnecessary.

Catalan normally uses the definite article with a specific person or role:

• la professora
• el metge
• la directora

So la professora here means the teacher.

But after certain verbs, especially when giving someone's profession or role, Catalan often omits the article:

• És professora. = She is a teacher.

So:

• La professora = the teacher
• És professora = she is a teacher

Because després normally takes de before a noun or infinitive.

So you say:

• després de l'examen = after the exam
• després de dinar = after lunch / after eating

So després de is the pattern you should learn.

Because examen starts with a vowel, and the masculine singular article el becomes l' before a vowel sound.

So:

• el llibre = the book
• l'examen = the exam

After de, you get:

• de + l'examen = de l'examen

Compare:

• del llibre = of the book / from the book
• de l'examen = of the exam / from the exam

So the apostrophe appears because el changes to l' before examen.

Because their functions are different:

• la resposta is the direct object: the thing that is explained
• els is the indirect object: the people who receive the explanation

A useful test is to ask:

• What does the teacher explain? → la resposta
• To whom does the teacher explain it? → els

So the sentence structure is:

• subject: La professora
• indirect object: els
• verb: explica
• direct object: la resposta
• time expression: després de l'examen

Then Catalan uses two pronouns together.

• la resposta → la
• els stays els

So you can get:

• La professora els l'explica després de l'examen.

This means The teacher explains it to them after the exam.

That pattern can feel tricky to English speakers, but it is very common in Catalan: the indirect object pronoun comes before the direct object pronoun.

Yes, Catalan word order is somewhat flexible, but your sentence has a very natural, neutral order.

You could also say:

• Després de l'examen, la professora els explica la resposta.

That simply puts the time expression first for emphasis or style.

But the original order is perfectly normal and probably the most straightforward for learners.

The accent mark shows the correct stress: the word is stressed on the last syllable.

So it is pronounced roughly like des-PRÉS.

Accents in Catalan are important because they often show:

• which syllable is stressed
• sometimes also the vowel quality

So després should be learned with the accent included.