Si el salero está vacío, mi padre usa el pimentero y luego me pide que los llene.

Because si without an accent means if.

Sí with an accent means yes or can be used for emphasis, as in sí, claro.

So here Si el salero está vacío... means If the salt shaker is empty...

Si introduces a condition: if the salt shaker is empty.

The speaker is describing what happens under that condition. In English, this is the normal choice too: If the salt shaker is empty, ...

Cuando means when or whenever, and in some repeated situations it can overlap a bit with si, but si focuses more clearly on the condition itself.

Spanish uses estar for states or conditions, and ser for more permanent or defining qualities.

Being empty is treated as a temporary state, so Spanish says:

• está vacío = it is empty
• está lleno = it is full

Using es vacío would sound unnatural here, because the salt shaker is not inherently an empty object; it just happens to be empty at that moment or in that situation.

Because vacío agrees with el salero, which is masculine singular.

In Spanish, adjectives usually agree in gender and number with the noun they describe:

• el salero vacío = the empty salt shaker
• la botella vacía = the empty bottle
• los recipientes vacíos = the empty containers

So here:

• salero = masculine singular
• vacío = masculine singular

In this sentence:

• salero = salt shaker / salt cellar / salt container
• pimentero = pepper shaker / pepper container

In everyday table context, both words refer to the containers used for salt and pepper.

Like many Spanish nouns, pimentero can have other meanings in other contexts, but here it clearly means the pepper container.

Because Spanish often uses the present tense to talk about habitual or repeated actions.

This sentence does not have to mean one single event happening right now. It can mean something like:

• Whenever the salt shaker is empty, my father uses the pepper shaker and then asks me to fill them.

So the present tense here expresses a general routine or repeated pattern.

This is the normal Spanish pattern for ask someone to do something:

• pedirle a alguien que + subjunctive

Here:

• me = to me
• pide = asks
• que los llene = that I fill them

So me pide que los llene literally means he asks me that I fill them, but in natural English it is he asks me to fill them.

Spanish usually does not use the English-style structure asks me to fill them directly. It prefers pedir que + subjunctive when one person asks another person to do something.

Because after pedir que, Spanish uses the subjunctive.

So:

• infinitive: llenar = to fill
• present subjunctive: llene

Here llene means I fill in a requested or non-factual sense:

• me pide que los llene = he asks me to fill them

It is not lleno, because lleno is either an adjective meaning full or a different verb form. It is not llena, because the implied subject here is yo, not ella/usted. It is not llenar, because Spanish needs a conjugated verb after que in this structure.

The subject is understood to be yo, but Spanish often leaves subject pronouns out when they are clear from the verb form and the context.

So:

• me pide que los llene
• understood: me pide que yo los llene

English usually needs I more often, but Spanish can omit yo because llene and the context already make the subject clear enough.

Los is the direct object pronoun meaning them.

In this sentence, it most naturally refers to the two containers mentioned: el salero and el pimentero.

Since both nouns are masculine singular, together they become masculine plural:

• el salero
  • el pimentero → los

So:

• los llene = fill them

If the nouns were feminine, Spanish would use las instead.

Because object pronouns usually go before a conjugated verb in Spanish.

Here llene is a conjugated verb, so Spanish says:

• los llene

This is normal with finite verbs, including the subjunctive.

Compare:

• que los llene = that I fill them
• llenarlos = to fill them

With an infinitive like llenar, the pronoun can attach to the end: llenarlos. But with a conjugated form like llene, it normally goes before: los llene.

Yes. Rellenar often means to refill, so me pide que los rellene would also make sense.

But llenar is perfectly natural here. Spanish often uses llenar where English might specifically say fill up or refill.

So both are possible, but llenar is very common and idiomatic.

Because the sentence begins with an if-clause, and Spanish normally separates that introductory clause with a comma:

• Si el salero está vacío, mi padre usa...

This is standard punctuation.

If the order were reversed, the comma is often omitted:

• Mi padre usa el pimentero si el salero está vacío.