Sempre que a campainha toca, o cão começa a latir.

Sempre que means whenever or every time that.

So Sempre que a campainha toca means Whenever the bell rings / Every time the bell rings.

It introduces a repeated or habitual situation, not a one-time event.

Sometimes yes, but the meaning changes a bit.

• Sempre que clearly means whenever / every time
• Quando usually just means when

So:

• Sempre que a campainha toca, o cão começa a latir.
  = Every time the bell rings, the dog starts barking.

• Quando a campainha toca, o cão começa a latir.
  can also work, especially in context, but it is less explicit about repetition.

If you want to make the habitual meaning very clear, sempre que is the better choice.

Because Portuguese uses definite articles much more often than English.

• a campainha = the bell / the doorbell
• o cão = the dog

In English, we might sometimes say Whenever bell rings, dog starts barking only in very unusual styles, but Portuguese normally wants the articles here.

So even when English might sound more general, Portuguese often still uses the-type words.

Not necessarily. The present tense here expresses a habitual action.

So toca does not mean the bell is ringing at this exact moment. It means that this is what usually happens.

The same is true of the whole sentence:

• Sempre que a campainha toca, o cão começa a latir.

This is like English:

• Whenever the bell rings, the dog starts barking.

Both languages often use the present tense for routines, habits, and repeated facts.

Yes. Tocar is the normal verb used for bells, phones, alarms, and similar sounds.

Examples:

• A campainha toca. = The bell rings.
• O telefone está a tocar. = The phone is ringing.

This is the same verb tocar that can also mean to touch or to play an instrument. Portuguese often uses one verb where English uses several different ones, so the exact meaning depends on context.

Because começar a latir means to start barking or to begin barking.

That is slightly different from simply saying:

• O cão late. = The dog barks.

Compare:

• O cão late quando ouve barulho.
  = The dog barks when it hears noise.

• O cão começa a latir quando a campainha toca.
  = The dog starts barking when the bell rings.

The version with começa a focuses on the beginning of the action.

Because the verb começar is normally followed by a + infinitive.

So:

• começar a latir = to start barking
• começar a falar = to start speaking
• começar a chover = to start raining

This is just the standard pattern you learn with começar.

Latir is a correct standard verb meaning to bark.

You may also hear ladrar. Both exist, and usage can vary by speaker or region. For a learner, the important point is:

• latir = to bark
• começar a latir = to start barking

So the sentence is completely natural and correct as it stands.

In European Portuguese, cão is the normal general word for dog.

Cachorro in Portugal more often means puppy.

So in this sentence, o cão is the natural choice in Portugal.

This is different from Brazilian Portuguese, where cachorro is very commonly used for dog in general.

Because Sempre que a campainha toca is an introductory subordinate clause.

The comma separates that clause from the main clause:

• Sempre que a campainha toca,
• o cão começa a latir.

This is very natural punctuation in Portuguese.

You can also reverse the order:

• O cão começa a latir sempre que a campainha toca.

In that version, the comma is usually not needed.

Yes. Cada vez que also means every time that.

So this is possible:

• Cada vez que a campainha toca, o cão começa a latir.

The difference is small:

• sempre que = whenever / every time
• cada vez que = each time / every time

Both are natural. Sempre que is slightly more compact and very common.

Not here. In this sentence, the speaker is talking about a regular, factual, repeated event, so the indicative is used:

• Sempre que a campainha toca...

If the meaning were more future-oriented or hypothetical, other structures might appear. But in this sentence, it is describing a normal repeated pattern, so toca is the correct choice.

Cão can be tricky for English speakers because of the nasal vowel.

A rough guide is:

• it starts like cow
• but the vowel is nasal, so the sound comes partly through the nose

It is not exactly like any normal English word.

Also, this word is useful to remember because its plural is irregular:

• cão = dog
• cães = dogs

So it is a good word to learn early, even though the pronunciation takes practice.