En cuanto empieza la firma de autores, hacemos cola.

Here en cuanto means as soon as.

It introduces the moment when the action in the main clause happens:

• En cuanto empieza la firma de autores, hacemos cola.
• As soon as the author signing starts, we line up.

A learner might compare it with cuando, which just means when. En cuanto is more immediate: it emphasizes that one thing happens right after the other.

In this sentence, empieza is in the present indicative because the sentence sounds like a habitual action or a regular sequence of events:

• Whenever / as soon as the signing starts, we line up.

So the idea is not a single future event, but something that normally happens.

If you were talking about a specific future occasion, Spanish would usually prefer the subjunctive:

• En cuanto empiece la firma de autores, haremos cola.
• As soon as the signing starts, we’ll line up.

So:

• empieza = usual / repeated situation
• empiece = future event not yet started

For the same reason: this sentence is describing a routine, a general habit, or what typically happens in that situation.

Spanish often uses the present tense for repeated actions:

• En cuanto empieza la firma de autores, hacemos cola.

This can mean something like:

• Whenever the signing starts, we line up.
• As soon as the signing starts, we usually line up.

If it were about one future event, you would more naturally say:

• En cuanto empiece la firma de autores, haremos cola.

Here firma does not mean just a written signature. It refers to a signing event, especially where writers sign books for readers.

So la firma de autores means something like:

• the author signing
• the authors’ signing session
• the book-signing event

In Spain, especially in contexts like book fairs, this use of firma is very common.

De autores is a more general label, like saying author signing or writers’ signing as a type of event.

Spanish often leaves out the article in this kind of category-style expression:

• feria de libros
• firma de autores
• tienda de ropa

If you said de los autores, it would sound more specific, as if you were talking about particular authors already identified in the conversation.

So:

• firma de autores = an author-signing event / author signings in general
• firma de los autores = the signing by the specific authors we’ve already mentioned

Yes, hacer cola is a fixed expression in Spanish meaning:

• to queue
• to stand in line
• to line up

So:

• hacemos cola = we queue / we stand in line

You normally do not translate it word for word as make a queue in English, even though that is how it is built in Spanish.

In Spain, hacer cola is very common. In many parts of Latin America, you may also hear hacer fila.

Because hacer cola is an idiomatic expression. In this phrase, cola appears without an article.

So the normal form is:

• hacer cola

not usually:

• hacer una cola

Compare similar fixed expressions:

• hacer fotos
• hacer ejercicio
• hacer cola

When Spanish uses a noun inside a fixed expression like this, it often drops the article.

The comma is natural and helpful, because the sentence begins with a subordinate time clause:

• En cuanto empieza la firma de autores, hacemos cola.

In Spanish, when this kind of clause comes first, a comma is commonly used to separate it from the main clause.

You may sometimes see sentences without the comma in informal writing, but using it here is standard and clear.

Yes, grammatically you could, but the nuance changes a little.

• En cuanto empieza... = as soon as it starts
• Cuando empieza... = when it starts

En cuanto gives a stronger sense of immediacy: the lining up happens right away.

So if you want to emphasize immediately after it begins, en cuanto is the better choice.

It is perfectly good Spanish, and one part of it sounds especially natural in Spain:

• hacer cola

That expression is extremely common in Spain. In other Spanish-speaking regions, people may be more likely to say:

• hacer fila
• ponerse en la fila
• ponerse en la cola in some places

Also, firma de autores is very natural in cultural contexts in Spain, such as book fairs or literary events.

Yes. Both are good, but they sound different depending on the variety of English:

• we queue = very natural in British English
• we line up / we get in line = more natural in American English

So hacemos cola can match several English translations depending on the learner’s variety of English.