Learn Hardcore Spanish (Spain): Hay una cola larguísima en la tienda porque empiezan las rebajas. - There is a very long line in the store because the sales are starting.

Hay una cola larguísima = “There is a very long queue.”
Es = “is” (identity/description): La cola es larguísima (“The queue is very long.”)
Está = “is” (location/state): La cola está en la tienda (“The queue is in the shop.”)

So:

Use hay when introducing or mentioning that something exists somewhere.
Use es/está when you’re talking about a specific, already-known thing.

Here the sentence is introducing the existence of a queue in the shop, so hay is correct.

What does cola mean in this context, and is it always “queue”?

In Spain, cola commonly means “queue / line of people”.

Other meanings:

cola = tail (of an animal)
Colloquially, it can refer to buttocks in some contexts.
For the drink Coke, you usually say Coca-Cola or refresco de cola, not just cola on its own.

In Spain, hacer cola = “to queue” / “to line up.”
In many Latin American countries, fila is more common than cola for “queue.”

What is larguísima and how is it formed?

Larguísima is an emphatic form of the adjective larga (“long”). It’s formed using the suffix -ísimo/-ísima, which intensifies the meaning, roughly “very / extremely / super”.

Formation:

Adjective: largo (long) → feminine: larga
Remove final -o/-a and add -ísimo/-ísima: larguísimo / larguísima

It must agree with the noun in gender and number:

una cola larguísima (feminine singular)
unos ríos larguísimos (masculine plural)

So cola is feminine singular, so the adjective must be larguísima.

What is the difference between muy larga and larguísima?

Both express that the queue is very long, but with a different feel:

muy larga = “very long” (neutral, standard emphasis)
larguísima = “really / extremely long”, more intense and expressive

Nuances:

larguísima can sound more emotional or dramatic.
muy larga is a bit more neutral and common in everyday speech.

Both are correct; larguísima just adds extra emphasis.

Why is the adjective placed after the noun: una cola larguísima and not una larguísima cola?

The normal position for descriptive adjectives in Spanish is after the noun:

una cola larga / larguísima (standard word order)

Putting the adjective before the noun is possible but often changes the nuance:

una larguísima cola would sound more emotional, literary, or emphatic, almost like “such a ridiculously long queue.”

In everyday speech, una cola larguísima is the most natural order.

Why is it en la tienda and not a la tienda?

en la tienda = “in the shop” or “at the shop” (location)
a la tienda = “to the shop” (direction / movement)

The sentence describes where the queue is, not where someone is going, so it uses en (location):

Hay una cola larguísima en la tienda.
There is a very long queue in/at the shop.

If it were about movement:

Voy a la tienda. = I’m going to the shop.

What does rebajas mean, and why is it plural?

In Spain, las rebajas means “the sales” (when shops reduce prices, usually in specific seasons).

Key points:

It is almost always used in the plural: las rebajas.
It refers to the general sales period, not just a single discounted item.

Cultural note (Spain):

rebajas de enero (January sales, after Christmas)
rebajas de verano (summer sales, usually July)

Related words:

descuentos = discounts
ofertas = offers / deals

So empiezan las rebajas = “the sales are starting / the sales period is beginning.”

Why is the verb empiezan in the plural?

The verb empiezan (they start) must agree with its subject:

Subject: las rebajas (plural)
Verb: empiezan (3rd person plural of empezar)

If the subject were singular, the verb would be singular:

La rebaja empieza. = The discount starts.

But in standard Spanish for seasonal sales, the phrase is las rebajas (plural), so we say empiezan.

Why does the sentence say empiezan las rebajas instead of las rebajas empiezan? Is there a difference?

Both orders are grammatically correct:

empiezan las rebajas
las rebajas empiezan

In this sentence, empiezan las rebajas is part of a porque clause explaining the reason:

…porque empiezan las rebajas.

In spoken Spanish, starting with the verb here sounds very natural and keeps the flow.
Las rebajas empiezan is also fine and maybe slightly more neutral or explicit.

There’s no important change in meaning; it’s more about rhythm and style.

Why is the present tense (empiezan) used here instead of a future form like van a empezar?

Spanish uses the present tense very often for events that are starting now or very soon:

Empiezan las rebajas.
Literally “the sales start,” but in context it can mean “are starting / are about to start.”

Alternatives:

Van a empezar las rebajas. = They are going to start (focus on near future).
Empezarán las rebajas. = They will start (more distant/factual future).

In the original sentence, the idea is that the sales are starting now or very soon, and that’s why people are already queuing, so present tense is natural and idiomatic.

Why not say están empezando las rebajas instead of empiezan las rebajas?

Both are possible, but they’re not used in the same way:

Empiezan las rebajas.
Simple statement: “The sales start” / “The sales are starting.” Very common in announcements, explanations, and headlines.
Están empezando las rebajas.
Emphasises the ongoing process right now: “The sales are (just) starting now.” It sounds more like describing what is happening at this very moment.

Spanish tends to use the simple present more than English where English uses continuous forms, so empiezan las rebajas is usually preferred.

Why is porque followed by the indicative (empiezan) and not the subjunctive?

Porque is giving a real, factual reason:

Hay una cola larguísima… porque empiezan las rebajas.
There is a very long queue because the sales are starting. (This is taken as a fact.)

With real reasons, Spanish uses the indicative:

porque llueve (because it’s raining)
porque no tengo tiempo (because I don’t have time)

You would only use a subjunctive after porque in certain special, more literary or ironic uses, or when it’s part of another structure (e.g. no porque… sino porque…). In everyday reasoning like this, the indicative empiezan is correct.

Why is there no subject pronoun in empiezan las rebajas? Shouldn’t it be ellas empiezan?

In Spanish, subject pronouns are usually omitted because the verb ending already shows the subject:

empiezan clearly indicates “they start” (3rd person plural).
las rebajas is the subject, so adding ellas is unnecessary.

You would use ellas only for emphasis or contrast:

Ellas empiezan mañana, no hoy.
They start tomorrow, not today.

In the original sentence, empiezan las rebajas is perfectly natural without any pronoun.