Mi abuela se pone a tararear en la cocina cuando oye a esa locutora por la radio.

Ponerse a + infinitive means to start/begin to do something.

So:

• tararea = she hums
• se pone a tararear = she starts humming / she begins to hum

This structure adds the idea that the action begins at that moment, usually as a reaction to something. In this sentence, the trigger is hearing that radio presenter.

In this expression, ponerse a + infinitive is a fixed pronominal structure.

• poner by itself usually means to put
• ponerse a + infinitive means to start doing something

So here se is not optional. You need it:

• Mi abuela se pone a tararear = My grandmother starts humming

Without se, pone would suggest the normal meaning of put, not begin.

Tararear means to hum, especially humming a tune or melody without fully singing the words.

It often suggests a soft, casual, absent-minded kind of singing. So it fits well with the idea of a grandmother in the kitchen reacting to something she hears on the radio.

Both verbs relate to hearing, but they are not exactly the same:

• oír = to hear
• escuchar = to listen to

In many cases, oír is about perceiving sound, while escuchar suggests more deliberate attention.

So:

• cuando oye a esa locutora = when she hears that radio presenter
• cuando escucha a esa locutora would sound more like when she listens to that presenter

Here, oye works naturally because the sentence focuses on the moment she hears the presenter’s voice.

That is the personal a.

In Spanish, when the direct object is a specific person or animate being, you usually use a before it.

So:

• oye a esa locutora

The grandmother is hearing a specific person: that female radio presenter. Because it is a specific human being, Spanish uses the personal a.

Compare:

• Oye la música = She hears the music
• Oye a la locutora = She hears the presenter

Esa is a demonstrative adjective meaning that.

In Spanish, the choice between esta, esa, aquella depends on psychological or physical distance:

• esta = this (close)
• esa = that (not close to the speaker)
• aquella = that over there / that one farther away

In this sentence, esa locutora simply means that presenter, someone not especially close to the speaker. It can sometimes also carry a slightly emotional tone, depending on context, but here it most likely just means that particular radio presenter.

Locutora is a feminine noun. It usually means a female announcer, radio presenter, or broadcaster.

In this sentence, because we have por la radio, the most natural interpretation is a female radio host/presenter/announcer.

The masculine form is locutor.

Por la radio means on the radio / over the radio / through the radio.

Spanish often uses por to express the medium through which something is heard, seen, or communicated.

So:

• oír a alguien por la radio = to hear someone on the radio

You may also hear en la radio in some contexts, but por la radio strongly emphasizes the medium or channel through which the voice is coming.

The present tense here expresses a habitual action or a general repeated situation.

So the sentence means something like:

• whenever this happens, she does that
• this is what she typically does

That is why Spanish uses:

• se pone
• oye

rather than a past tense. It presents the situation as a regular pattern.

After cuando, Spanish uses:

• indicative for habitual actions, present facts, or things seen as real
• subjunctive for future or not-yet-real events

Here the sentence describes a repeated, real situation:

• cuando oye a esa locutora = when she hears that presenter

This is a habitual fact, so oye is in the indicative.

Compare:

• Cuando oye a esa locutora, se pone a tararear.
  = Whenever she hears that presenter, she starts humming.

• Cuando oiga a esa locutora, se pondrá a tararear.
  = When she hears that presenter in the future, she will start humming.

Yes. Spanish word order is flexible, especially with adverbial phrases like en la cocina.

The original sentence is perfectly natural:

• Mi abuela se pone a tararear en la cocina cuando oye a esa locutora por la radio.

But you could also say:

• Mi abuela, cuando oye a esa locutora por la radio, se pone a tararear en la cocina.
• En la cocina, mi abuela se pone a tararear cuando oye a esa locutora por la radio.

The basic meaning stays the same, though the emphasis changes slightly. In the original, en la cocina simply gives the setting in a natural, neutral way.

Yes. Mi abuela is the subject.

The verb forms agree with that subject:

• se pone = third person singular
• oye = third person singular

Both actions refer to my grandmother:

• she starts humming
• she hears that presenter

So the structure is:

• Mi abuela = subject
• se pone a tararear = main action
• en la cocina = place
• cuando oye a esa locutora por la radio = time clause

Oye is pronounced roughly like OH-yeh.

A few pronunciation notes:

• The oy sounds similar to the beginning of English boy, but shorter and smoother.
• The y in oye sounds like the y in yes.
• In Spain, it is generally pronounced clearly as two syllables: o-ye.

Yes, you could.

• cuando oye a esa locutora = when she hears that presenter
• al oír a esa locutora = on hearing that presenter / when she hears that presenter

Both are grammatical. The version with cuando is more straightforward and neutral.
The version with al + infinitive is also common, but it can sound a little more compressed or stylistically shaped.

So:

• Mi abuela se pone a tararear en la cocina cuando oye a esa locutora por la radio.
• Mi abuela se pone a tararear en la cocina al oír a esa locutora por la radio.

Both work, but the original is very natural and easy to understand.