Il collare è accanto alla pettorina.

Because Italian nouns have grammatical gender.

• collare is masculine singular, so it takes il
• pettorina is feminine singular, so it takes la

So:

• il collare = the collar
• la pettorina = the harness

You usually need the article in Italian in a sentence like this.

Because alla is a contraction.

It comes from:

• a
  • la = alla

Since pettorina is feminine singular, the article is la, and after the preposition a, they combine into alla.

This is very common in Italian:

• a + il = al
• a + la = alla
• a + i = ai
• a + le = alle

Accanto means next to or beside.

In Italian, it is commonly used as accanto a, so the full structure is:

• accanto a = next to / beside

Because the next word is la pettorina, a + la becomes alla, giving:

• accanto alla pettorina

So the sentence structure is literally something like:

• The collar is beside the harness

The accent is important because è and e are different words.

• è = is
• e = and

So in this sentence, è is the verb essere in the he/she/it is form.

The accent helps distinguish it clearly from e.

Yes. È is the third-person singular form of essere, which means to be.

In this sentence:

• Il collare = subject
• è = is
• accanto alla pettorina = next to the harness

So the basic pattern is:

• subject + essere + place/location

Yes, but the normal, neutral word order is:

• Il collare è accanto alla pettorina.

That is the most natural way to say it in everyday Italian.

You may sometimes hear different word order for emphasis, for example:

• Accanto alla pettorina c’è il collare.

That changes the focus slightly and sounds more like Next to the harness, there is the collar.

For a learner, the original order is the safest and most standard.

You normally need the articles, so Collare è accanto a pettorina sounds wrong in standard Italian.

Italian uses articles much more often than English does. In a sentence like this, the natural form is:

• Il collare è accanto alla pettorina.

Omitting the articles would sound incomplete or unnatural.

Yes. Vicino a is another very common way to say near or close to.

So you could say:

• Il collare è vicino alla pettorina.

The difference is slight:

• accanto a often suggests right next to
• vicino a can mean near, sometimes a little less exact

In many everyday situations, both are fine.

A useful approximate pronunciation for English speakers is:

• pet-to-REE-na

A few details:

• the tt is pronounced more strongly than a single t
• the stress is on ri: pettoRIna
• the r is an Italian r, ideally tapped or lightly rolled

So the rhythm is:

• pet-to-RI-na

Yes, these nouns have fixed grammatical gender:

• il collare = masculine
• la pettorina = feminine

That means the article and any adjectives referring to them must match that gender and number.

For example:

• il collare rosso = the red collar
• la pettorina rossa = the red harness

So the gender matters not just for the article, but for agreement too.