Learn Hardcore Spanish (Latin America): Mi abuelo cuenta su historia en voz baja antes de dormir. - My grandfather tells his story in a low voice before sleeping.

contar has two main meanings:
- to tell / to relate (a story, an anecdote, etc.)
  - Mi abuelo cuenta su historia. = My grandfather tells his story.
- to count (numbers)
  - Mi abuelo cuenta hasta diez. = My grandfather counts to ten.

In this sentence it clearly means to tell. The full form is:

él cuenta = he tells / he is telling

Why is it cuenta and not something like dice or habla?

Spanish has several verbs that translate as to say / to tell / to speak, but they’re used differently:

contar = to tell / narrate a story or series of events
- contar una historia, contar un chiste (tell a story / a joke)
decir = to say / to tell (a specific piece of information or words)
- decir la verdad, decir algo, decir una frase
hablar = to speak / to talk (more general)
- hablar de política, hablar con mi abuelo

Since the sentence is about narrating a story, contar (→ cuenta) is the most natural verb.

What tense is cuenta, and does it mean he does it right now or regularly?

Cuenta is present tense: él cuenta = he tells / he is telling.

In Spanish, the simple present can express:

a habitual action: something that happens regularly
- In this context, it likely means:
  My grandfather (usually) tells his story in a low voice before going to sleep.
or an action happening right now (depending on context).

So the sentence can describe a routine (most natural reading) or a current situation; context would decide.

Why is it su historia and not something like una historia?

su historia = his story (or her/their story, depending on context)
una historia = a story

Using su tells us it is a specific story belonging to someone, presumably the grandfather. The sentence emphasizes his own story, not just any random story he might tell.

If you want to make it very clear that it is his own personal story, you can also say:

Mi abuelo cuenta su propia historia… = My grandfather tells his own story…

Does su historia always mean “his story”? Can it also mean “her/their story”?

Yes, su is ambiguous by itself:

su historia can mean his story, her story, their story, or your (formal) story.

In this sentence, context (the presence of mi abuelo) makes it most natural to understand it as his story.

If you need to remove ambiguity, you can say:

la historia de mi abuelo = my grandfather’s story
su historia, la de mi abuelo = his story, my grandfather’s

What does the phrase en voz baja mean literally and idiomatically?

Literally:

en voz baja = in a low voice

Idiomatic meaning:

quietly, softly, in a low voice, not loudly

It is a very common fixed expression in Spanish. Some related examples:

Habla en voz baja. = Speak quietly.
El niño lee en voz alta. = The child reads aloud / in a loud voice.

Why is it en voz baja and not something like bajamente?

Spanish often prefers prepositional phrases instead of adverbs in -mente to describe how someone speaks.

Natural: en voz baja, en voz alta, en silencio
Very rare / odd: bajamente (almost never used in this sense)

So en voz baja is the normal, idiomatic way to say in a low voice / softly.

Why is it antes de dormir and not antes de que duerme?

Spanish uses two different patterns:

Same subject for both actions → antes de + infinitive
- Mi abuelo cuenta su historia antes de dormir.
  The person who tells and sleeps is the same (the grandfather), so we use:
  - antes de + dormir (infinitive)
Different subjects → antes de que + subjunctive
- Mi abuelo cuenta su historia antes de que nosotros durmamos.
  (he tells, we sleep)

So antes de dormir is correct because both actions refer to the grandfather.

In English I’d say “before going to sleep.” Is antes de dormir the same as before going to sleep?

Yes, very similar.

antes de dormir literally: before sleeping
Natural English equivalent: before going to sleep or before he goes to sleep

Both express the same idea of what happens right before he falls asleep.

Why is there no él in Mi abuelo cuenta…? Could I say Él cuenta su historia…?

Spanish usually omits subject pronouns because the verb ending already shows the subject.

cuenta already implies he / she / it tells.
Mi abuelo makes the subject clear, so él is not needed.

You can say:

Él cuenta su historia…, but it often sounds redundant here.
Subject pronouns (yo, tú, él, nosotros, etc.) are normally used only for emphasis or contrast:
Él cuenta su historia, no yo. = He tells his story, not me.

Can the word order change? For example, can I say Mi abuelo cuenta en voz baja su historia antes de dormir?

Yes, you can move en voz baja and su historia around without changing the basic meaning. All of these are grammatical:

Mi abuelo cuenta su historia en voz baja antes de dormir.
Mi abuelo cuenta en voz baja su historia antes de dormir.
Mi abuelo, en voz baja, cuenta su historia antes de dormir. (more written / dramatic)

The most neutral and common in everyday speech is probably the original:

Mi abuelo cuenta su historia en voz baja antes de dormir.

Could I say Mi abuelo se duerme instead of dormir? What’s the difference?

Yes, but the structure changes:

Mi abuelo cuenta su historia antes de dormirse.
- dormirse (reflexive) = to fall asleep
- Focus on the moment of falling asleep.
Mi abuelo cuenta su historia antes de dormir.
- dormir (non‑reflexive) = to sleep (in general)
- In practice, here it also means before he goes to sleep / before he falls asleep, and is very natural.

Both are acceptable in this context; antes de dormir is slightly more common and simpler.