Learn Hardcore Spanish (Spain): Me pongo nervioso cuando tengo que hablar en público. - I get nervous when I have to speak in public.

poner on its own means to put / to place.
ponerse (with a reflexive pronoun like me, te, se) often means to become / to get (in terms of mental or physical state).

So me pongo nervioso literally means I put myself nervous, which in natural English is I get nervous or I become nervous.

You need me because the subject yo (I) is affecting itself:

Yo me pongo nervioso = I get nervous.
Without me, pongo would need a direct object:
Pongo el libro en la mesa = I put the book on the table.

What is the difference between me pongo nervioso and estoy nervioso?

Both involve being nervous, but the focus is different:

Me pongo nervioso = I get nervous / I become nervous
- Focus on the change from not nervous → nervous.
- Often used for reactions in specific situations:
  - Me pongo nervioso cuando tengo examen.
Estoy nervioso = I am nervous
- Describes your current state, not the process of becoming that way.
- Example:
  - Estoy nervioso ahora mismo.

In the sentence Me pongo nervioso cuando tengo que hablar en público, the idea is: whenever that situation happens, I end up getting nervous.

Why is it nervioso and not nerviosa? What would a woman say?

Nervioso is an adjective and must agree in gender and number with the subject.

Here, the (implicit) subject is yo. The reflexive pronoun me refers to that yo.

If a man is speaking:
- (Yo) me pongo nervioso.
If a woman is speaking:
- (Yo) me pongo nerviosa.

More examples:

Nos ponemos nerviosos (a group of men or mixed group)
Nos ponemos nerviosas (a group of women)

Can ponerse be used with other emotions or physical states?

Yes. Ponerse + adjective is very common in Spanish to talk about sudden or temporary changes in emotional or physical states.

Examples:

Me pongo triste = I get sad.
Me pongo contento / contenta = I get happy.
Me pongo rojo / roja = I turn red / I blush.
Se pone nervioso cuando conduce = He gets nervous when he drives.

It often corresponds to to get or to become + adjective in English.

Why is the verb pongo (present tense) and not a past tense like puse or ponía?

The present tense pongo here is the habitual present: it expresses something that generally happens, a repeated pattern.

Me pongo nervioso cuando tengo que hablar en público.
= I (always / generally) get nervous when I have to speak in public.

If you talked about a specific past situation, you would change the tense:

Me puse nervioso cuando tuve que hablar en público.
= I got nervous when I had to speak in public (that one time).

So pongo is present because you are talking about what usually happens whenever that situation occurs.

Why is it tengo que hablar and not something like debo hablar?

Both are possible, but they are not used in exactly the same way.

Tener que + infinitive = to have to do something (very common, neutral obligation)
- Tengo que hablar en público = I have to speak in public.
Deber + infinitive = should / ought to / must (duty, recommendation, sometimes moral obligation)
- Debo hablar en público = I should speak in public / I must speak in public (more formal, slightly different nuance).

In everyday Spanish (including Spain), tener que is more common to express practical obligation (work, school, tasks), so tengo que hablar en público sounds very natural.

Could you say tengo hablar en público without que?

No. In Spanish, tener expressing obligation must be followed by que:

Correct: tengo que hablar en público
Incorrect: tengo hablar en público

The structure is always:

tener que + infinitive
- Tengo que estudiar.
- Tenemos que salir.
- Tienen que trabajar.

Why is it cuando tengo que hablar and not cuando tenga que hablar with the subjunctive?

Both are possible, but they mean different things.

In your sentence:

Me pongo nervioso cuando tengo que hablar en público.
- Tengo (indicative) is used for a general, habitual fact.
- It means: whenever I have to speak in public (in general), I get nervous.

Use indicative after cuando when:

You are talking about general habits or things that are seen as real and regular.

Use subjunctive after cuando when:

The event is future / not yet realized / uncertain:
- Me pondré nervioso cuando tenga que hablar en público.
  = I will get nervous when I have to speak in public (in the future).
- Cuando tengas que hablar en público, avísame.
  = When you have to speak in public, let me know.

So in your original sentence, the indicative tengo is correct because it describes a recurring, real situation.

Can I change the word order to start with cuando?

Yes. Both orders are fine and mean the same:

Me pongo nervioso cuando tengo que hablar en público.
Cuando tengo que hablar en público, me pongo nervioso.

Starting with cuando is often used to set the scene first, then give the reaction, but there is no change in meaning here.

Why is it hablar en público and not hablar al público?

They mean different things:

Hablar en público
- Literally: to speak in public
- Means to speak in front of people / an audience, in general.
- Focus on the situation of speaking where others are present.
Hablar al público
- Literally: to speak to the public
- Emphasises the audience as a group you address.
- It can sound more specific or formal, like addressing the public as a defined group.

In the sense of public speaking as a situation that makes someone nervous, the natural and fixed expression is hablar en público.

Why is there no article in en público (not en el público)?

En público is a fixed expression meaning in public / in front of others. In this expression, público is used without an article.

en público = in public (as opposed to privately)

If you say en el público, it sounds like you are physically inside the audience, which is not the intended meaning here and is not idiomatic in this context.

So:

hablar en público = speak in public
besarse en público = to kiss in public

Could I say me pongo muy nervioso? Is that more natural?

Yes, adding muy is very natural and common:

Me pongo nervioso cuando tengo que hablar en público.
Me pongo muy nervioso cuando tengo que hablar en público.
= I get very nervous when I have to speak in public.

Both are correct; muy just emphasizes the intensity.

Can I attach me to poner instead, like cuando tengo que ponerme a hablar en público?

Yes, but the meaning changes slightly:

Me pongo nervioso cuando…
- Focus on becoming nervous.
Cuando tengo que ponerme a hablar en público…
- ponerme a + infinitive = to start / begin to do something.
- Literally: when I have to start speaking in public…

You could combine ideas:

Me pongo nervioso cuando tengo que ponerme a hablar en público.
= I get nervous when I have to start speaking in public.

In your original sentence, me pongo nervioso is about the emotional reaction, and tengo que hablar is the obligation. The pronoun me belongs with pongo, not with hablar.