Learn Hardcore Spanish (Latin America): Pongo un cojín en el sillón y otro en la silla para mi abuela. - I put one cushion on the armchair and another on the chair for my grandmother.

So Pongo un cojín... literally means “I put a cushion…”.
If you said Poner un cojín…, it would be like saying “To put a cushion…”, which is not a complete sentence.

Could I also say Estoy poniendo un cojín en el sillón…?

Yes, you can, but the nuance changes a bit.

Pongo un cojín… = I put / I am putting a cushion…
Used for habitual actions or for a present action in a neutral way. Spanish often uses the simple present instead of the progressive.
Estoy poniendo un cojín… = I am (right now) putting a cushion…
Emphasizes that the action is happening at this very moment.

Both are grammatically correct. In many everyday contexts where English uses “I’m putting”, Spanish is perfectly happy with Pongo.

Why is it un cojín and not una cojín?

Because cojín is masculine in Spanish, so it takes the masculine article un.

un cojín = a cushion (masculine)
una silla = a chair (feminine)
mi abuela = my grandmother (feminine noun, but the possessive mi doesn’t change)

Even though cojín ends in -ín, that doesn’t make it feminine. Many nouns ending in -ín are masculine (el jardín, el botín, el cojín). You just need to memorize the gender.

What’s the difference between cojín and almohada?

In Latin American Spanish:

cojín = cushion / throw pillow / seat or back cushion
Used on chairs, sofas, armchairs, benches, etc.
almohada = pillow for sleeping, the one on your bed

So in this sentence, cojín is correct because it’s something you put on a sillón or silla for comfort, not a bed pillow.
You might also see almohadón in some countries for a big cushion.

What is the difference between sillón and silla (and sofá)?

silla = a regular chair (often hard, usually without padding, often without armrests)
sillón = an armchair, a big, comfortable, padded chair (often with armrests)
sofá = a sofa/couch (usually for more than one person)

In Latin America, sillón is typically a single-seat armchair, while sofá is a longer couch.
So:

un cojín en el sillón = a cushion on the armchair
otro en la silla = another on the (regular) chair

Why is it en el sillón and not sobre el sillón?

Both en and sobre can sometimes be translated as “on”, but:

en is very general: in / on / at.
sobre is more specific: on top of.

In everyday speech, en is far more common in sentences like this:

Pongo un cojín en el sillón.
= I put a cushion on the armchair.

You could say sobre el sillón, but it sounds more formal or more physically precise. The natural, default choice here is en.

Why is it el sillón but la silla?

This is about grammatical gender:

el sillón – masculine noun → masculine article el
la silla – feminine noun → feminine article la

Gender doesn’t always follow a simple rule based on the ending, but some patterns exist:

Nouns ending in -a are often feminine (la silla, la casa).
Nouns ending in -ón are often masculine (el sillón, el corazón, el avión), though there are exceptions.

So you must learn each noun with its article: el sillón, la silla.

Why is it otro and not un otro cojín?

In Spanish, otro already includes the idea of “another / one more”, so you don’t add un before it:

otro cojín = another cushion / one more cushion
❌ un otro cojín – ungrammatical in standard Spanish

So the sentence correctly says:

…y otro en la silla… = “…and another one on the chair…”

Why don’t we repeat en before la silla? Why not “…en el sillón y en la silla”?

Spanish often omits repeated prepositions when they apply to parallel elements with the same verb:

Pongo un cojín en el sillón y otro en la silla.
(Here en is understood before la silla.)

You could say:

Pongo un cojín en el sillón y en la silla.

That’s also correct, but it slightly changes the focus:

en el sillón y otro en la silla emphasizes that they are two different cushions in two different places.
en el sillón y en la silla could suggest the same action/location pattern more than the “one here and another there” contrast.

Both are grammatically fine; the original sounds very natural and clear.

Why is it para mi abuela and not a mi abuela?

Para and a can both be used in “for/to someone” ideas, but they behave differently.

Para often expresses purpose, benefit, or destination:
- Pongo un cojín… para mi abuela.
  = I put a cushion… for my grandmother (for her comfort/benefit).
A is normally used for indirect objects (with a pronoun):
- Le pongo un cojín en el sillón a mi abuela.
  Literally: I put a cushion on the armchair to my grandmother (for her).

In your sentence, there is no indirect object pronoun (le), so para mi abuela is the natural way to show that the purpose/beneficiary is your grandmother.

Both para mi abuela and a mi abuela can be correct, but the structure has to match:

Pongo un cojín… para mi abuela. ✅
Le pongo un cojín… a mi abuela. ✅

Why is it mi abuela without an accent, and not mí abuela?

Spanish has two different words:

mi (no accent) = my (possessive adjective)
- mi abuela = my grandmother
mí (with accent) = me (stressed pronoun after a preposition)
- para mí = for me

In your sentence:

para mi abuela = for my grandmother (possessive)
Using mí abuela would be wrong, because mí never goes directly before a noun.

Can I change the word order, like Para mi abuela pongo un cojín…?

Yes, Spanish allows flexible word order, but it changes emphasis:

Pongo un cojín en el sillón y otro en la silla para mi abuela.
Neutral order, most common.
Para mi abuela pongo un cojín en el sillón y otro en la silla.
Emphasizes “For my grandmother” (that’s the important part).
Pongo, para mi abuela, un cojín en el sillón…
Also possible, a bit more formal or written-style.

All are grammatically correct; the original version is the most typical in conversation.

How do you pronounce sillón and what does the accent mark do?

In most of Latin America:

sillón is pronounced roughly like see-YON:
- si = “see”
- ll = usually like English y (in many areas), sometimes like zh/j in others
- ón = “on” with a nasal n, stressed

The accent mark in sillón shows where the stress goes:

Words ending in a vowel, n, or s are normally stressed on the second-to-last syllable.
Without an accent, sillon would be stressed as SI-llon.
With the accent (sillón), the stress moves to the last syllable: si-LLÓN.

The same thing happens with cojín:

cojín ≈ co-HEEN (the j is like a harsh English h)
The accent on í tells you to stress the last syllable.