Respirar hondo me calma los nervios antes de la entrevista.

Because respirar hondo is being used as a general action, like breathing deeply in English.

In this sentence, respirar hondo acts as the subject of the verb:

• Respirar hondo = breathing deeply
• me calma = calms me

So the structure is basically:

• Breathing deeply calms my nerves before the interview.

If you said Respiro hondo, that would mean I breathe deeply or I am breathing deeply, which would create a different sentence.

It is singular because the subject is the whole action respirar hondo, and that action is treated as one thing.

So:

• Respirar hondo = one action
• therefore calma = singular verb

This is similar to English:

• Breathing deeply calms me not
• Breathing deeply calm me

Here hondo means deeply.

Spanish often uses expressions like:

• respirar hondo = to breathe deeply
• dormir bien = to sleep well
• hablar claro = to speak clearly

So even though hondo is literally an adjective meaning deep, in this expression it works naturally with respirar and sounds very idiomatic.

You could say respirar profundamente, and it would be understood, but respirar hondo is more common and natural in everyday Spanish.

The me shows who is affected: me = to me / for me.

The sentence has both:

• me = the person affected
• los nervios = the thing being calmed

So me calma los nervios literally works like:

• it calms the nerves for me or more naturally:
• it calms my nerves

In Spanish, this kind of structure is very common with body parts, emotions, and personal effects.

Spanish often uses the definite article (el, la, los, las) instead of a possessive like mi/mis when it is already clear whose thing is being talked about.

Because the sentence already includes me, it is obvious that the nerves are my nerves.

So Spanish prefers:

• me calma los nervios

rather than:

• me calma mis nervios

Using mis nervios is not impossible, but it is usually less natural here.

In this sentence, los nervios means nerves / nervousness / anxiety, not the physical nerves in your body.

It is a very common expression:

• tener nervios
• estar de los nervios
• me calman los nervios

So here it refers to the emotional state of being nervous, especially before something stressful like an interview.

Because antes normally needs de before a noun.

So:

• antes de la entrevista = before the interview
• antes de comer = before eating
• antes de salir = before leaving

Without de, it would be incorrect in this sentence.

Using la entrevista suggests a specific interview that the speaker and listener already know about, or that is clear from context.

So:

• antes de la entrevista = before the interview

If you said:

• antes de una entrevista

that would mean before an interview in a more general sense, not necessarily one specific interview.

Yes, very often it can.

By itself, entrevista can mean interview in general:

• a job interview
• a media interview
• an interview for a school or program

In many everyday contexts, especially with nervios, people will often understand it as a job interview unless context suggests something else.

Yes, that is grammatically correct, but it changes the nuance slightly.

• Respirar hondo me calma los nervios sounds more natural and personal in Spanish.
• Respirar hondo calma mis nervios is understandable, but it sounds a bit less idiomatic in everyday speech.

Spanish often prefers the pattern:

• me + verb + article + body part / emotion-related noun

So me calma los nervios is the more typically Spanish way to say it.

Yes. Spanish word order is flexible.

For example, you could also say:

• Antes de la entrevista, respirar hondo me calma los nervios.

This puts more emphasis on before the interview.

You could even hear:

• Me calma los nervios respirar hondo antes de la entrevista.

That structure is also correct, though it may sound a little more stylistic or emphatic depending on context.

Yes, very common.

It means:

• to calm someone’s nerves
• to reduce nervousness

Examples:

• Un té me calma los nervios.
• Hablar con ella me calma los nervios.
• Respirar hondo me calma los nervios.

It is a useful everyday phrase, especially for talking about stress, anxiety, or pre-event tension.