Nos esforzamos mucho para terminar el informe antes de la reunión.

Because the verb is esforzarse, which is a reflexive verb meaning to make an effort / to try hard.

The full infinitive is esforzarse:

• me esfuerzo = I make an effort
• te esfuerzas = you make an effort
• se esfuerza = he/she makes an effort
• nos esforzamos = we make an effort
• os esforzáis = you all make an effort
• se esfuerzan = they make an effort

So nos matches we.

Nos esforzamos means we make an effort, we try hard, or we put in a lot of effort.

A useful thing to know: this form can be understood as either:

• present: we try hard / we make an effort
• preterite: we tried hard / we made a big effort

In real life, context usually makes it clear which one is meant.

Because this sentence is using the indicative, not the subjunctive.

The verb here is conjugated for nosotros:

• infinitive: esforzarse
• present indicative: nos esforzamos

You would use esforcemos in different structures, such as:

• Es importante que nos esforcemos. = It’s important that we make an effort.

But in your sentence, the speaker is simply stating a fact, so nos esforzamos is the normal choice.

Mucho here works like an adverb and means a lot.

So:

• Nos esforzamos mucho = We tried hard / We made a big effort

In Spanish, adverbs like this often come after the verb:

• trabaja mucho = he works a lot
• estudian mucho = they study a lot
• nos esforzamos mucho = we try hard

Because para + infinitive is a very common way to express purpose in Spanish.

So:

• para terminar el informe = in order to finish the report

It answers the question for what purpose?

• Nos esforzamos mucho para terminar el informe...
• We tried hard in order to finish the report...

Normally, no.

Use para when you mean in order to / with the goal of:

• Nos esforzamos mucho para terminar el informe.

Por usually expresses other ideas, such as:

• cause: Lo hice por ti. = I did it because of you / for you.
• means: por email = by email
• duration or movement through places, etc.

So in this sentence, para is the natural choice because it expresses the goal of the effort.

Because after para, Spanish normally uses an infinitive when the subject stays the same.

Here, the people making the effort and the people finishing the report are the same people:

• Nos esforzamos mucho para terminar el informe.

If the subject changed, Spanish would often need a different structure, for example:

• Nos esforzamos mucho para que ellos terminaran el informe. = We tried hard so that they would finish the report.

So para + infinitive is correct here because we are the ones finishing it.

Spanish often uses the definite article more than English does.

So:

• el informe = the report

Even when English might sometimes sound natural without an article in certain contexts, Spanish usually keeps it:

• terminar el informe
• abrir la puerta
• lavarse las manos

In this sentence, el informe refers to a specific report that both speaker and listener know about.

Because antes normally needs de when it is followed by a noun.

So:

• antes de la reunión = before the meeting
• antes de comer = before eating

Without de, it would sound incomplete or incorrect here.

Because de + el contracts to del, but de + la does not contract.

Here the noun is feminine:

• la reunión

So:

• de la reunión = correct

Compare:

• antes del informe = before the report
• antes de la reunión = before the meeting

Also note that reunión is feminine, so it takes la.

Antes de is used before:

• a noun: antes de la reunión
• an infinitive: antes de salir

Examples:

• antes de la reunión = before the meeting
• antes de terminar = before finishing

Antes que is used before a conjugated verb, often in more formal or specific structures:

• Antes que empiece la reunión... = Before the meeting starts...

So in your sentence, because la reunión is a noun phrase, antes de is the correct choice.

Yes. Reunión has a written accent because of Spanish stress rules.

It is pronounced roughly reh-oo-NYON, with the stress on the last syllable.

The accent mark tells you where the stress goes:

• reunión

It is also a feminine noun:

• la reunión
• una reunión

Yes, Spanish word order is flexible, although some orders sound more neutral than others.

The most neutral version is:

• Nos esforzamos mucho para terminar el informe antes de la reunión.

But you could also say:

• Para terminar el informe antes de la reunión, nos esforzamos mucho.
• Antes de la reunión, nos esforzamos mucho para terminar el informe.

These versions shift the emphasis a little, but the basic meaning stays the same.

Yes. Nos esforzamos can be ambiguous out of context.

It can mean:

• we make an effort / we try hard = present
• we made an effort / we tried hard = preterite

Spanish has several forms where the nosotros present and preterite look identical.

Context tells you which meaning is intended:

• if someone is describing what is happening now, it is probably present
• if they are telling a past story, it is probably preterite

Yes. Instead of translating it word for word, it is often best to think of esforzarse as:

• to make an effort
• to try hard
• to put in effort

So:

• Nos esforzamos mucho can feel more natural as
  • We tried really hard
  • We put in a lot of effort

That is usually more helpful than thinking too literally about the structure.