Quando ti avvicini alla stalla, il cavallo ti guarda.

Because the verb here is avvicinarsi, which means to approach / to get closer.

It is a pronominal/reflexive-style verb, so it normally includes a reflexive pronoun:

• mi avvicino = I approach / I get closer
• ti avvicini = you approach / you get closer
• si avvicina = he/she approaches

So in this sentence, ti avvicini means you approach or you get closer.

Even though it looks reflexive, it does not literally mean you approach yourself. In Italian, some verbs simply use these pronouns as part of their normal form.

The two ti forms do different jobs:

• ti avvicini: here ti is part of the verb avvicinarsi
• ti guarda: here ti means you as the object of guarda

So:

• ti avvicini = you approach
• ti guarda = it looks at you

This is very common in Italian. The same pronoun form can appear twice in a sentence with different grammatical roles.

Alla is a contraction of a + la:

• a = to
• la = the
• alla = to the

The verb avvicinarsi is usually followed by a when you say what someone is approaching:

• avvicinarsi alla casa = to approach the house
• avvicinarsi al cavallo = to approach the horse
• avvicinarsi alla stalla = to approach the stable

So alla stalla means to the stable.

Because avvicinarsi normally takes a before the place or thing you move closer to.

Examples:

• Mi avvicino alla porta. = I move closer to the door.
• Si avvicina al cane. = He/She approaches the dog.
• Ti avvicini alla stalla. = You approach the stable.

This is just the standard pattern of the verb, and it does not match English word-for-word.

Italian usually leaves out subject pronouns when they are clear from the verb ending.

• avvicini already tells us the subject is tu
• guarda already tells us the subject is lui/lei or a singular noun like il cavallo

So Quando ti avvicini alla stalla naturally means When you approach the stable without needing tu.

You could say Quando tu ti avvicini alla stalla, but that would usually add emphasis or contrast, and it is less neutral.

Italian often uses the present tense for things that are generally true, habitual, or happen whenever a situation occurs.

So this sentence can mean something like:

• When you approach the stable, the horse looks at you
• Whenever you approach the stable, the horse looks at you

It describes a regular or typical action, not necessarily something happening only right now.

It can suggest either, depending on context.

In a sentence like this, with the present tense and a general meaning, quando often has the sense of when/whenever:

• Quando ti avvicini alla stalla, il cavallo ti guarda.

This sounds like a repeated or usual situation: each time you approach the stable, the horse looks at you.

So in practice, an English speaker might understand it as whenever even though the Italian word is quando.

The clause beginning with Quando comes first:

• Quando ti avvicini alla stalla = subordinate time clause
• il cavallo ti guarda = main clause

In Italian, it is very common to use a comma when this kind of introductory clause comes before the main clause.

If you reverse the order, the comma is often unnecessary:

• Il cavallo ti guarda quando ti avvicini alla stalla.

Both versions are correct. The version with the quando clause first puts a little more focus on the situation or timing.

Mostly yes here, but there is a small structure difference.

Italian says:

• guardare qualcuno = to look at someone

English usually needs at:

• The horse looks at you

Italian does not use a separate word for at here. The object pronoun goes directly with the verb:

• ti guarda = looks at you

So literally, Italian is more like the horse sees/looks you, but natural English is looks at you.

Italian uses articles much more often than English.

So il cavallo is the normal way to say the horse. In context, it could refer to:

• a specific horse already known in the situation, or
• the horse associated with that stable

Leaving out the article here would sound incomplete in standard Italian.

Yes. Stalla is the normal word for a stable or animal stall/building, especially in farm contexts.

Depending on context, English might also say barn, but stalla specifically points to the place where animals are kept. In a sentence with il cavallo, stable is the most natural match.

Yes. Italian word order is flexible, although some versions are more neutral than others.

A very natural alternative is:

• Il cavallo ti guarda quando ti avvicini alla stalla.

This means the same thing.

The original version:

• Quando ti avvicini alla stalla, il cavallo ti guarda.

puts more emphasis on the time/situation first: when you approach the stable...

So the difference is mainly one of focus, not basic meaning.

The common intransitive meaning to approach / to get closer is normally avvicinarsi.

Examples:

• Mi avvicino. = I come closer.
• Si avvicina alla finestra. = He/She approaches the window.

There is also avvicinare without the reflexive pronoun, but that usually means to bring something closer or to move something nearer.

For example:

• Avvicino la sedia al tavolo. = I move the chair closer to the table.

So in your sentence, ti avvicini is the correct form because you are the one moving closer.