La professora ens explica la resposta després de la classe.

Ens means us or to us here.

In this sentence, la resposta is the thing being explained, and ens shows who receives the explanation:

• La professora = the teacher
• ens = to us
• explica = explains
• la resposta = the answer

Catalan object pronouns like ens usually go before a conjugated verb:

• Ens explica la resposta. = She explains the answer to us.

That is different from English, where us usually comes after the verb.

Because explica is the conjugated form of the verb, while explicar is the infinitive.

The verb is explicar = to explain.

Here the subject is La professora (the teacher), which is third person singular, so in the present tense you get:

• jo explico = I explain
• tu expliques = you explain
• ell/ella explica = he/she explains

So:

• La professora ens explica... = The teacher explains to us...

Catalan often drops subject pronouns when they are not needed.

So instead of saying:

• Ella ens explica la resposta...

it is very natural to say:

• La professora ens explica la resposta...

Or even just:

• Ens explica la resposta...

if the context already makes it clear who she is.

This is normal in Catalan, just like in Spanish or Italian.

They are both the feminine singular definite article, meaning the.

• la professora = the teacher
• la resposta = the answer

Both professora and resposta are feminine singular nouns, so they both take la.

This is completely normal. English also repeats the:

• The teacher explains the answer...

Because professora is the feminine form, and professor is the masculine form.

• el professor = the male teacher
• la professora = the female teacher

Catalan often marks gender clearly in profession words.

So if the teacher is a woman, la professora is correct.

Because Catalan normally places weak object pronouns like ens before the conjugated verb.

So Catalan says:

• ens explica la resposta

Literally, that looks like:

• to us explains the answer

But that is just normal Catalan structure.

A very common pattern is:

• Subject + object pronoun + verb + direct object

For example:

• La professora ens explica la lliçó.
• El pare em compra un llibre.
• La mare li escriu una carta.

Després de means after when it is followed by a noun phrase.

So:

• després de la classe = after class / after the class

This is a fixed pattern:

• després de + noun
• després de + infinitive

Examples:

• després de la feina = after work
• després de dinar = after eating / after lunch

You normally cannot just say després la classe. The de is needed.

Because de + la stays de la.

Catalan contractions happen with some combinations, especially:

• de + el = del
• a + el = al

But with la, there is no contraction:

• de la classe = correct
• del classe = incorrect

So:

• després de la classe is exactly what you want.

In this sentence, la classe most naturally means the class/lesson.

So:

• després de la classe = after class / after the lesson

If you want to talk specifically about the physical room, Catalan often uses l’aula:

• a l’aula = in the classroom

That said, classe can sometimes refer to the class session or the group, depending on context.

Yes, but not in exactly the same way.

• ens is the normal unstressed object pronoun: to us
• a nosaltres is a stressed form: to us

In ordinary sentences, ens is the usual choice:

• La professora ens explica la resposta.

If you use a nosaltres, it usually adds emphasis or contrast:

• La professora ens explica la resposta a nosaltres, no a ells.
  = The teacher explains the answer to us, not to them.

So ens is the basic form, and a nosaltres is more emphatic.

It is the present tense, and like the present tense in many languages, it can have different uses depending on context.

It can mean:

• a general/habitual action:
  La professora ens explica la resposta després de la classe.
  = The teacher explains the answer to us after class. / The teacher usually explains it to us after class.

• something happening now or around now, depending on context

Catalan present tense is often quite flexible, just like English explains / is explaining in some contexts.

The accent mark shows where the stress goes.

• després

The stress falls on the final syllable: -prés.

In Catalan, written accents help you know pronunciation and sometimes vowel quality as well. Even if you do not yet know all the pronunciation rules, the accent tells you that this word does not follow the default stress pattern.

So the accent is there to guide pronunciation.

The given order is very natural and standard:

• La professora ens explica la resposta després de la classe.

Catalan does allow some flexibility, especially for emphasis, but not every change sounds equally natural.

For example, you could also say:

• Després de la classe, la professora ens explica la resposta.

This puts emphasis on when it happens.

But the original sentence is the safest and most neutral order for a learner.