Envia un missatge a la professora si tens una pregunta sobre la classe.

Yes. Envia is the informal singular imperative of enviar (to send). It is used when speaking to one person that you would address as tu.

So:

• enviar = to send
• (tu) envia = send!

This matches tens later in the sentence, which is also the tu form.

Catalan often leaves out subject pronouns because the verb ending already shows who the subject is.

So instead of saying:

• Tu envia un missatge...

Catalan normally just says:

• Envia un missatge...

And instead of:

• si tu tens una pregunta

it usually says:

• si tens una pregunta

The forms envia and tens already make it clear that the sentence is addressing tu.

Because tens is the second person singular form of tenir (to have), used with tu:

• jo tinc = I have
• tu tens = you have
• ell/ella té = he/she has

Since the whole sentence is addressed informally to one person, tens is the correct form.

The phrase a la professora means to the teacher. The preposition a is used to mark the recipient of the message.

So:

• un missatge = a message
• a la professora = to the teacher

This is similar to English send a message to the teacher.

Catalan uses definite articles very naturally, often more than English does.

Here:

• la professora = the teacher
• la classe = the class

The article is used because the speaker means a specific teacher and a specific class, not just any teacher or any class.

This is a very important distinction:

• si = if
• sí = yes

In this sentence, si tens una pregunta means if you have a question, so it must be si without an accent.

Sobre means about or regarding.

So:

• una pregunta sobre la classe = a question about the class

This is a very common way to express topic or subject matter in Catalan. In many contexts, sobre works much like English about.

Because un is the indefinite article, meaning a.

• un missatge = a message

Without the article, the phrase would sound incomplete or unnatural in this context. Catalan usually needs the article here just as English does.

Yes, in meaning it is. Pregunta means question.

It comes from the verb:

• preguntar = to ask

So the pattern is:

• preguntar = to ask
• una pregunta = a question

This is a useful word family to learn together.

The structure is:

• Envia = command verb
• un missatge = direct object
• a la professora = recipient / indirect object
• si tens una pregunta sobre la classe = conditional clause

So literally the order is:

• Send a message to the teacher if you have a question about the class.

This word order is very natural in Catalan.

Yes. This sentence is informal because it uses tu forms: envia and tens.

A more formal version, addressing someone as vostè, would be:

• Enviï un missatge a la professora si té una pregunta sobre la classe.

Compare:

• envia / tens = informal singular
• enviï / té = formal singular

So the original sentence is the kind of thing you would say to a student, friend, or someone you address with tu.