La professora és exigent, però explica molt bé la lliçó.

Catalan usually uses ser (és) for a person’s more permanent or characteristic qualities, and estar for temporary states or conditions.

So in La professora és exigent, the idea is that being demanding is part of the teacher’s character or teaching style.

• és exigent = she is demanding
• està cansada = she is tired

Using està exigent would sound unusual in most normal contexts.

Professora is the feminine form of professor.

Because the teacher is female, Catalan uses:

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

The article also changes to match the noun:

• la with feminine singular nouns
• el with masculine singular nouns

Some Catalan adjectives have the same form for masculine and feminine. Exigent is one of them.

So you get:

• el professor és exigent
• la professora és exigent

But other adjectives do change, for example:

• el professor és estricte
• la professora és estricta

So exigent is just an adjective with one form for both genders.

In this sentence, exigent is not directly modifying the noun inside the noun phrase. It comes after és, so it is a predicate adjective.

Structure:

• La professora = subject
• és = verb
• exigent = adjective describing the subject

This works much like English The teacher is demanding.

If an adjective directly modifies a noun, Catalan often puts it after the noun too, although placement can vary depending on meaning and style.

Però means but.

It connects two contrasting ideas:

• La professora és exigent
• però explica molt bé la lliçó

So the contrast is: the teacher is demanding, but she explains the lesson very well.

The accent in però shows the stressed vowel and helps indicate pronunciation.

• però is pronounced with stress on the second syllable

In standard Catalan, this is the normal spelling. The accent is part of the word; it is not optional.

Catalan word order here is very natural:

• explica = explains
• molt bé = very well
• la lliçó = the lesson

So:

• explica molt bé la lliçó

The adverb phrase molt bé usually goes after the verb. This is similar to English explains the lesson very well, although Catalan is often a bit more flexible with word order than English.

You could also hear:

• explica la lliçó molt bé

Both are possible, but explica molt bé la lliçó sounds very natural.

In this sentence, molt bé is correct because bé is the adverb meaning well.

• explica molt bé = explains very well

You may also see ben, but it is used differently, often before adjectives or participles:

• ben fet = well done
• ben explicat = well explained

So here, because it modifies the verb explica, bé is the right form.

Catalan often uses the definite article naturally with nouns where English may or may not use one, especially when talking about something specific.

Here la lliçó means the lesson, referring to the lesson being explained.

• explica la lliçó = explains the lesson

This is completely normal Catalan. In many contexts, leaving out the article would sound incomplete or unnatural.

Lliçó can look tricky because it contains two very Catalan-looking features:

• ll
• ç

A rough pronunciation is something like lyi-SO or, depending on accent, close to yi-SO.

A few details:

• ll is traditionally a palatal sound, similar to the lli in some pronunciations of Spanish ll or the lli in million, though exact comparisons are imperfect.
• ç is pronounced like s before a, o, u.
• The accent in ó shows the stressed syllable: lli-ÇÓ.

So lliçó is stressed on the last syllable.

Catalan often leaves out subject pronouns because the verb form already gives enough information.

• explica already tells you it is he/she/it explains
• és already tells you he/she/it is

Since la professora is already the subject, adding ella is unnecessary.

Catalan usually includes subject pronouns only for emphasis, contrast, or clarity.

For example:

• La professora és exigent, però ella explica molt bé la lliçó.

This is possible, but it adds emphasis to she.

Yes. That would mean The teacher is very demanding.

Compare:

• és exigent = is demanding
• és molt exigent = is very demanding

In your original sentence, molt modifies bé, not exigent:

• explica molt bé = explains very well

So be careful where molt goes, because it changes what is being intensified.

In Catalan, it is normal to place a comma before però when it links two main clauses.

So this punctuation is standard:

• La professora és exigent, però explica molt bé la lliçó.

It works much like English ..., but ....

Yes, depending on context.

For teacher:

• professora is very common, especially for a school or secondary-school teacher
• mestra can also mean a female teacher, especially in primary education

For lesson:

• lliçó often means a lesson in the sense of material being taught
• classe means class, and that is a different idea

So explica molt bé la lliçó focuses on explaining the lesson/content well, not necessarily on running the class well.