El veterinario llega mañana.

Because el veterinario is the subject of the sentence, and in Spanish a singular countable noun usually needs a determiner such as el, un, este, etc.

• El veterinario llega mañana. = The veterinarian arrives tomorrow.
• Un veterinario llega mañana. = A veterinarian arrives tomorrow.

You can leave out the article in some other situations, such as after ser:

• Es veterinario. = He/She is a veterinarian.

But in this sentence, as the subject, veterinario normally needs el.

Grammatically, veterinario is the masculine form. The feminine form is veterinaria.

• El veterinario = the male veterinarian
• La veterinaria = the female veterinarian

In many real contexts, if you know the vet is a woman, you would usually say la veterinaria. If the sentence says el veterinario, learners should normally understand it as masculine.

The infinitive is llegar, which means to arrive.

Llega is the third-person singular present-tense form:

• yo llego
• tú llegas
• él/ella/usted llega

It ends in -a because it is an -ar verb in the present tense, third-person singular.

So llega can mean:

• he arrives
• she arrives
• it arrives
• you arrive (formal usted)

In this sentence, it matches el veterinario, so it means the veterinarian arrives.

Spanish often uses the present tense to talk about a planned or expected future event, especially when there is a time word like mañana.

So:

• El veterinario llega mañana.

is completely natural and means something like:

• The veterinarian is arriving tomorrow
• The veterinarian arrives tomorrow

English does this too in some contexts:

• My flight leaves tomorrow.

Spanish could also use a future form:

• El veterinario llegará mañana.

Both are correct, but the present tense often sounds very natural for scheduled future events.

Because llegar means to arrive, while venir means to come.

• El veterinario llega mañana. = The veterinarian arrives tomorrow.
• El veterinario viene mañana. = The veterinarian comes tomorrow.

Sometimes both could work in similar situations, but they are not exactly the same:

• llegar focuses on reaching the destination
• venir focuses on movement toward the speaker or a reference point

So if the original sentence uses llega, the focus is on the veterinarian’s arrival.

Because mañana here is used as a time expression meaning tomorrow, and Spanish often uses these time words directly without a preposition.

Examples:

• llega mañana = arrives tomorrow
• salimos hoy = we leave today
• vuelven el lunes = they return on Monday

This is similar to English, where you also usually say tomorrow, not on tomorrow.

In this sentence, mañana is being used as an adverb of time, so it means tomorrow.

That is very common:

• Llega mañana. = He/She arrives tomorrow.

When mañana means morning, it is usually a noun and often appears with an article or in a phrase:

• la mañana = the morning
• por la mañana = in the morning

So:

• El veterinario llega mañana. = tomorrow
• El veterinario llega por la mañana. = in the morning

Yes. Spanish word order is more flexible than English.

You could also say:

• Mañana llega el veterinario.

This still means the same thing, but it puts more focus on mañana.

In general:

• El veterinario llega mañana. = neutral, straightforward order
• Mañana llega el veterinario. = emphasizes tomorrow

Both are natural.

A natural Latin American pronunciation is approximately:

el beh-teh-ree-NAH-ryoh YEH-gah ma-NYAH-nah

A few key sounds:

• v in veterinario is usually pronounced very similarly to b in Spanish
• r in veterinario is a tapped/flapped r
• ll in llega is often pronounced like an English y sound in much of Latin America
• j in llega is a strong breathy sound, like a stronger English h
• ñ in mañana sounds like ny in canyon

So llega is often close to YEH-gah in many Latin American accents, though pronunciation varies by region.

Yes, el usually points to a specific or known veterinarian: the veterinarian.

Compare:

• El veterinario llega mañana. = the veterinarian arrives tomorrow
• Un veterinario llega mañana. = a veterinarian arrives tomorrow

So if the speaker says el veterinario, they usually mean a particular vet that both speaker and listener can identify from context.

Yes. In normal English, the most natural translation may sometimes use is coming even if the Spanish verb is llegar.

That is because languages do not always match word-for-word. Depending on context:

• El veterinario llega mañana. could be rendered as
  • The veterinarian arrives tomorrow.
  • The vet is coming tomorrow.

But grammatically, the Spanish verb here is still llegar = to arrive. The English wording may shift a little to sound natural.