En cuanto comienza la cuenta regresiva, entramos.

Here en cuanto means as soon as.

It is similar to cuando (when), but en cuanto is more specific: it emphasizes that one action happens immediately after another.

• En cuanto comienza la cuenta regresiva, entramos.
  = We go in as soon as the countdown begins.

Compare:

• Cuando comienza la cuenta regresiva, entramos.
  = When the countdown begins, we go in.

This also works, but en cuanto sounds more immediate.

A very important note:

• en cuanto = as soon as
• en cuanto a = as for / regarding

Those are different expressions.

Because Spanish often uses the present tense for actions that are generally true, habitual, scheduled, or understood as part of a sequence.

In this sentence, comienza can sound like:

• a general rule
• a planned sequence
• a vivid narration

So En cuanto comienza la cuenta regresiva, entramos can mean something like:

• As soon as the countdown starts, we go in
• As soon as the countdown starts, we’re going in

Spanish does this more freely than English.

Also, comienza is:

• 3rd person singular
• present tense
• from comenzar

It matches la cuenta regresiva, which is singular.

For the same basic reason: Spanish often uses the present tense to talk about a planned or expected future action, especially in instructions, routines, or sequences.

So:

• En cuanto comienza la cuenta regresiva, entramos.

can naturally mean:

• As soon as the countdown starts, we go in
• As soon as the countdown starts, we’re going in

If you said:

• En cuanto comience la cuenta regresiva, entraremos

that would also be correct, but it sounds more explicitly future-oriented and a bit more formal or carefully structured.

So the original sentence sounds more direct and natural in many contexts.

Both word orders are correct.

• En cuanto comienza la cuenta regresiva, entramos.
• En cuanto la cuenta regresiva comienza, entramos.

The first version is usually more natural. Spanish often places the verb before the subject in this kind of sentence, especially when introducing an event:

• comienza la cuenta regresiva
• llega el tren
• empieza la película

It gives the sentence a smooth, natural flow.

Because the verb ending tells you.

Entramos means we enter / we go in.

Spanish often leaves out subject pronouns because the verb already shows the person and number:

• entro = I enter
• entras = you enter
• entra = he/she/it enters
• entramos = we enter
• entran = they enter

So nosotros is not necessary unless you want emphasis or contrast.

For example:

• Nosotros entramos, pero ellos esperan.
  = We go in, but they wait.

In the original sentence, the subject is understood without needing nosotros.

Because its subject is la cuenta regresiva, which is singular.

• la cuenta regresiva = singular
• therefore: comienza

If the subject were plural, the verb would also be plural:

• En cuanto comienzan las alarmas, entramos.
  = As soon as the alarms start, we go in.

Spanish verbs must agree with their subject in number and person.

Yes. La cuenta regresiva is a standard and widely understood way to say countdown in Latin America.

It is a feminine noun phrase:

• la cuenta = the count
• regresiva = backward / counting down

You may also hear el conteo regresivo in some contexts, but la cuenta regresiva is extremely common and natural.

Yes. In most everyday contexts, empezar and comenzar mean basically the same thing: to begin / to start.

So this is also natural:

• En cuanto empieza la cuenta regresiva, entramos.

In many situations, empezar sounds slightly more common in everyday speech, while comenzar can sound a little more formal or polished, but both are very normal.

The comma separates the introductory time clause from the main clause.

• En cuanto comienza la cuenta regresiva = subordinate clause
• entramos = main clause

So the comma helps show the structure clearly.

When the time clause comes first, Spanish often uses a comma:

• Cuando llegue, te llamo.
• Si llueve, no salimos.
• En cuanto empieza, entramos.

If the main clause comes first, the comma is often omitted:

• Entramos en cuanto comienza la cuenta regresiva.

That depends on the meaning.

If you are talking about a future event that has not happened yet, Spanish very often uses the present subjunctive after expressions like en cuanto:

• En cuanto comience la cuenta regresiva, entraremos.

This is a very standard future-oriented structure.

So why does the original sentence use comienza instead?

Because the present indicative can still appear if the speaker is presenting the action as:

• a routine
• a plan
• a vivid immediate sequence
• something seen as practically certain in a procedural way

So:

• En cuanto comienza la cuenta regresiva, entramos.
  sounds like a rule, script, or real-time sequence.

• En cuanto comience la cuenta regresiva, entraremos.
  sounds more like a future event being referred to in a more formal or neutral way.

Both can be correct; the choice depends on context and style.

It could be any of those, depending on context.

Spanish present tense is flexible, so the sentence may mean:

1. Habitual action

   • Whenever the countdown starts, we go in.

2. Planned future action

   • As soon as the countdown starts, we’re going in.

3. Narrative / dramatic present

   • The countdown starts, and we go in.

Without more context, all three are possible. Native speakers rely on the situation to understand which one is meant.

Yes, but it is not exactly the same.

• En cuanto comienza la cuenta regresiva, entramos.
  = As soon as the countdown begins, we go in.

• Al comenzar la cuenta regresiva, entramos.
  = On beginning / when the countdown begins, we go in.

Al comenzar can sound a bit more literary, compressed, or formal.
En cuanto is more explicit and conversational for as soon as.

So en cuanto is usually the best choice if you want to emphasize immediacy.