La professora explica tot abans de l'examen.

La is the feminine singular definite article, meaning the. So la professora means the teacher.

In Catalan, if you mean a specific teacher, you normally use the article. Leaving it out would not sound natural here.

Professora is the feminine form, so it refers to a female teacher.
Professor is the masculine form.

So:

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

Explica is the 3rd person singular present indicative of explicar.

It matches la professora because that subject is singular:

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

So here explica means explains or, depending on context, is explaining.

Yes. In Catalan, the simple present often covers both ideas.

So explica can mean:

• explains
• is explaining

If Catalan speakers want to be especially explicit about an ongoing action, they can also use a progressive form, but the simple present is very common.

Catalan often leaves out subject pronouns because the verb form usually makes the person clear, or the subject is already stated.

Here the subject is already given as la professora, so adding ella would be unnecessary.

That is very normal in Catalan.

Yes. Here tot is being used as a pronoun meaning everything.

So:

• explica tot = explains everything

This is different from:

• tothom = everyone

A common English-speaking learner mistake is to confuse everything and everyone. In this sentence, tot is correct because the meaning is everything.

Because here tot is not agreeing with a noun like an adjective would. It is being used on its own as a pronoun meaning everything.

Compare:

• tot = everything
• tota la classe = the whole class
• tots els llibres = all the books

So in this sentence, tot is the right form.

Abans de means before when it is followed by a noun or an infinitive.

So:

• abans de l'examen = before the exam
• abans de sortir = before leaving

Abans by itself can mean before/earlier, but in this structure Catalan needs de.

Because the article el changes to l' before a vowel.

So:

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

After de, you get:

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

So de l'examen is correct because examen begins with a vowel.

Because the sentence is talking about a specific exam: the exam.

Catalan uses the definite article here just as English does in before the exam.

If you wanted to say before an exam in a general sense, you would say:

• abans d'un examen

No, this is a very normal, neutral Catalan word order:

• La professora = subject
• explica = verb
• tot = object
• abans de l'examen = time expression

So it follows the common subject + verb + object + time phrase pattern.

You can move parts around for emphasis, for example:

• Abans de l'examen, la professora explica tot.

But the original sentence is the most straightforward version.