Llamamos al bombero.

Because Spanish normally uses the personal a before a specific person who is the direct object of the verb.

Here, el bombero is the person receiving the action of llamar, so Spanish says:

llamamos a el bombero

But a + el always contracts to al, so the correct form is:

Llamamos al bombero.

So the a here is not an extra word you translate directly into English; it is a normal grammatical feature of Spanish with people.

Because a + el must contract to al in standard Spanish.

So:

• a el → incorrect here
• al → correct

This contraction is automatic, just like:

• de + el → del

But note that this only happens with el, not with la, los, or las:

• a la bombera
• a los bomberos
• a las bomberas

It can mean either one.

For regular -ar verbs, the nosotros form in the present and the preterite is often identical:

• llamamos = we call / we are calling
• llamamos = we called

Context tells you which one is meant:

• Hoy llamamos al bombero. = Today we call / are calling the firefighter.
• Ayer llamamos al bombero. = Yesterday we called the firefighter.

So if you only see Llamamos al bombero, the form itself is ambiguous.

It is built into the verb ending.

In llamamos, the ending -amos tells you the subject is nosotros (we). Because of that, Spanish often leaves subject pronouns out when they are not needed.

So these both mean the same thing:

• Llamamos al bombero.
• Nosotros llamamos al bombero.

The version without nosotros is more natural in many situations.

Yes, absolutely.

Adding nosotros is grammatically correct, but it is usually done only when you want:

• emphasis
• contrast
• clarity

For example:

• Nosotros llamamos al bombero, no ellos.
  We called the firefighter, not them.

Without special emphasis, Spanish usually prefers simply:

Llamamos al bombero.

Yes. The verb is the same: llamar.

But the structure is different:

• llamar a alguien = to call someone
• llamarse = to be called / to be named

So:

• Llamamos al bombero. = We call/called the firefighter.
• Me llamo Ana. = My name is Ana / I am called Ana.

That is why learners often recognize llamar from me llamo, but here it is being used in its non-reflexive form.

Because bombero here is a specific, known person, so Spanish uses the article el.

You are not talking about any firefighter at all, but the firefighter. So Spanish says:

al bombero = a + el bombero

If you removed the article, the sentence would sound incomplete or unnatural in this context.

You would normally say:

Llamamos a la bombera.

A few things change:

• bombero → bombera
• al disappears, because a + la does not contract

So:

• al bombero = to/called the male firefighter
• a la bombera = to/called the female firefighter

In standard grammar, you would usually say:

Lo llamamos.

That is because al bombero is the direct object, and the standard direct-object pronoun for a singular masculine noun is lo.

However, in much of Spain, you may also hear:

Le llamamos.

This is due to leísmo, which is common in Spain, especially for a masculine person. So for Spain Spanish:

• Lo llamamos = standard and always safe
• Le llamamos = very common in many parts of Spain

If you are learning standard grammar, lo is the safest answer to remember first.

The normal, neutral order is:

Llamamos al bombero.

Spanish word order is more flexible than English, so Al bombero llamamos is possible, but it sounds marked or emphatic. It might suggest contrast or focus, something like:

It was the firefighter that we called.

So for an ordinary statement, stick with:

Llamamos al bombero.

In most of Spain, ll is pronounced like the y sound in English yes, so llamamos sounds roughly like ya-MA-mos.

However, pronunciation varies:

• In many areas, ll and y sound the same.
• In some regions or speakers, ll may have a slightly different sound.

For most learners of Spain Spanish, pronouncing llamamos with a y-like sound is a good, natural choice.