Todavía me queda por enviar el mensaje a mi amiga para preguntarle si se apunta al documental o a la comedia.

Todavía here means still or yet: it shows that this task has not been done so far.

So Todavía me queda por enviar... means something like I still have left to send...

A few useful points:

• todavía is very common in everyday Spanish.
• aún could also be used here with the same meaning.
• Putting it at the beginning gives it a natural setting-the-scene feel: As of now, this is still pending.

This is a very common Spanish structure:

• quedar = to remain / to be left
• quedar por + infinitive = to remain to be done

So:

• Me queda por enviar el mensaje = I still have the message left to send

It is slightly different from tengo que enviar el mensaje:

• tengo que enviar = I have to send
• me queda por enviar = I still haven’t sent it; it’s one of the things left to do

The second one focuses more on something being still pending.

Because the subject is el mensaje, not I.

Literally, the structure is closer to:

• The message remains for me to send

So:

• el mensaje = subject
• queda = third person singular, agreeing with el mensaje
• me = tells you to whom it remains

If the subject were plural, you would get quedan:

• Todavía me quedan dos mensajes por enviar.

Here me is an indirect object pronoun, and it means something like to me or for me.

So me queda is not it stays me or anything like that. It means:

• it remains for me
• I still have left

This use of an indirect object pronoun is very common with verbs like quedar:

• Me queda mucho trabajo. = I still have a lot of work left.
• Nos quedan dos días. = We have two days left.

Because after quedar, Spanish normally uses por + infinitive to mean still left to do.

So:

• quedar por enviar
• quedar por hacer
• quedar por resolver

all mean remain to be sent/done/resolved.

By contrast, para + infinitive usually expresses purpose:

• Lo hago para ayudarte. = I do it to help you.

So in this sentence:

• por enviar = the action still pending
• para preguntarle = the purpose of sending the message

That contrast is important.

El mensaje suggests a specific message that is already understood in the context.

So the speaker is not talking about just any message, but about the message they already know they need to send.

Compare:

• Tengo que enviar un mensaje a mi amiga. = I need to send a message to my friend.
  
  • less specific, maybe introducing the idea
• Tengo que enviar el mensaje a mi amiga. = I need to send the message to my friend.
  
  • a particular message already known

Para means in order to or to, expressing purpose.

So:

• para preguntarle = to ask her

The le refers to mi amiga.

A useful grammar point:

• preguntar algo a alguien = to ask someone something
• The person asked is often expressed with le

So:

• preguntarle = to ask her
• preguntarle si... = to ask her whether / if...

Because preguntar is in the infinitive.

In Spanish, object pronouns are attached to:

• infinitives
• gerunds
• affirmative commands

So:

• preguntarle
• decírselo
• escribiéndome

That is why you get preguntarle, not le preguntar.

If there were a conjugated verb plus an infinitive, Spanish sometimes allows two positions:

• Voy a preguntarle
• Le voy a preguntar

Both are possible there. But in para preguntarle, attaching it is the normal form.

In Spain, apuntarse a is a very common expression meaning:

• to join
• to sign up for
• to be up for
• to come along to

So here si se apunta al documental o a la comedia means something like:

• whether she’s up for the documentary or the comedy
• whether she wants to come along to the documentary or the comedy

This is very natural in Spain Spanish.

Also, the verb is reflexive:

• apuntarse a algo

Without se, apuntar usually means something else, such as:

• to write down
• to note
• to point

So se apunta is an idiomatic expression, not a literal reflexive in the English sense.

Yes, very much so. In Spain, apuntarse a is extremely common in casual speech.

For example:

• ¿Te apuntas? = Are you in? / Do you want to join?
• Me apunto. = I’m in.

In other Spanish-speaking regions, people may also understand it, but other expressions can be more common depending on the country, such as:

• sumarse
• anotarse
• ir
• querer venir

Since you’re learning Spanish from Spain, se apunta is absolutely a useful phrase to learn.

Because this si introduces an indirect yes/no question, not a condition.

Here the speaker is asking:

• whether she’s up for it

After this kind of si, Spanish normally uses the indicative:

• No sé si viene.
• Pregúntale si quiere venir.
• Quiero saber si se apunta.

So si se apunta is exactly what you would expect.

This is different from cases where English learners overexpect the subjunctive just because there is uncertainty. In Spanish, uncertainty alone does not automatically trigger the subjunctive.

Because al is the contraction of a + el.

So:

• a + el documental → al documental
• a + la comedia stays a la comedia

There is no contraction with la.

This a comes from the expression apuntarse a:

• apuntarse al documental
• apuntarse a la comedia

Because in Spanish, when you are referring to specific options like the documentary and the comedy, the definite article is very natural.

So:

• al documental
• a la comedia

sounds normal and complete.

Leaving out the articles would sound unnatural here. Spanish uses articles more often than English in many cases, especially when referring to known options, categories, or planned activities.

It is natural, but it is definitely the kind of sentence that strings several ideas together:

1. Todavía me queda por enviar el mensaje a mi amiga
2. para preguntarle
3. si se apunta al documental o a la comedia

Spanish often does this very comfortably.

If you wanted, you could split it into shorter sentences:

• Todavía me queda enviarle el mensaje a mi amiga. Quiero preguntarle si se apunta al documental o a la comedia.

But the original sentence is perfectly normal and natural in everyday Spanish.