Pongo la correa, el collar y el arnés sobre la mesa.

Pongo is the first-person singular present tense form of poner.

So it means:

• I put
• I place
• sometimes I’m putting, depending on context

Poner is an irregular verb, and pongo is one of its irregular present forms.

Examples:

• Pongo el libro en la mochila. = I put the book in the backpack.
• Pongo la mesa. = I set the table.

Because Spanish often omits subject pronouns when they are not needed.

The ending -o in pongo already tells you the subject is I. So yo is usually unnecessary.

• Pongo la correa... = normal, natural
• Yo pongo la correa... = possible, but usually adds emphasis, contrast, or clarity

For example:

• Yo pongo la correa y tú abres la puerta.
  Here yo and tú are used for contrast.

Because each noun has its own grammatical gender in Spanish.

• la correa → feminine
• el collar → masculine
• el arnés → masculine

In Spanish, you normally learn a noun together with its article:

• la correa
• el collar
• el arnés

That helps you remember the gender correctly.

Repeating the article is very natural in Spanish, especially when you mean specific items.

So la correa, el collar y el arnés sounds like:

• the leash
• the collar
• and the harness

Spanish often repeats articles in lists more readily than English does.

You may sometimes see article omission in other contexts, but in a sentence like this, repeating the article is standard and clear.

Because arnés is simply a masculine noun: el arnés.

Unfortunately, noun gender in Spanish is not always predictable just from the ending. Many endings give clues, but not all nouns follow a simple pattern. The safest approach is to learn the noun with its article:

• el arnés
• plural: los arneses

So instead of memorizing just arnés, memorize el arnés.

Here sobre la mesa means on the table or on top of the table.

Sobre often indicates position on a surface.

So:

• Pongo la correa... sobre la mesa. = I put the leash... on the table.

A similar expression is:

• encima de la mesa = on top of the table

In some situations, people may also say en la mesa, but sobre la mesa is more clearly on the surface of the table.

Also, remember that sobre can mean about/regarding in other contexts, but here it is clearly a location word.

Because in Spanish, as in normal English style, you usually do not use a comma before the final y in a simple list.

So this is standard:

• la correa, el collar y el arnés

Not usually:

• la correa, el collar, y el arnés

A comma before y is only used in special cases, such as avoiding confusion or adding extra information.

Yes. Spanish word order is flexible, although the original sentence is a very neutral, natural order.

Original:

• Pongo la correa, el collar y el arnés sobre la mesa.

Other possible versions:

• Sobre la mesa pongo la correa, el collar y el arnés.
• Pongo sobre la mesa la correa, el collar y el arnés.

These are all grammatical, but they can slightly change the emphasis:

• starting with Sobre la mesa emphasizes where
• starting with Pongo is more neutral

It can mean either one, depending on context.

The Spanish present tense can express:

• a habitual action: I put
• an action happening now: I’m putting

So Pongo la correa... could mean:

• I put the leash, the collar, and the harness on the table
• or I’m putting the leash, the collar, and the harness on the table

If you want to be very explicit about an action happening right now, Spanish can also use:

• Estoy poniendo la correa, el collar y el arnés sobre la mesa.

But the simple present is still very common and natural.

No. They refer to different items.

• correa = leash, lead, or strap depending on context
• collar = collar
• arnés = harness

Because all three appear together, the context is probably pet equipment.

So in this sentence:

• correa is most likely a leash
• collar is the item around the animal’s neck
• arnés is the body harness

Yes, but the meaning changes slightly.

• pongo = I put / I place
  This is the most general and everyday choice.

• coloco = I place / I position
  This can sound a little more careful, deliberate, or formal.

• dejo = I leave / I set down
  This often suggests that you leave the objects there.

Examples:

• Coloco la correa, el collar y el arnés sobre la mesa.
  = I place the leash, the collar, and the harness on the table.

• Dejo la correa, el collar y el arnés sobre la mesa.
  = I leave the leash, the collar, and the harness on the table.

So pongo is the most neutral and broadly useful option.

The accent mark shows where the stress goes:

• ar-NÉS

Without the accent mark, Spanish pronunciation rules would suggest a different stress pattern. The written accent tells you the final syllable is stressed.

A useful detail:

• singular: arnés
• plural: arneses

In the plural, the written accent disappears because the stress pattern changes naturally:

• ar-NE-ses