Usamos el compostador para peladuras y posos de café.

Because Spanish often leaves out subject pronouns when they are clear from the verb ending.

• Usamos already tells you the subject is we
• So Usamos el compostador... is completely natural
• Nosotros usamos el compostador... is also correct, but it adds emphasis, contrast, or clarity

For example:

• Usamos el compostador, pero ellos no. = We use the composter, but they don’t.

Yes. Usamos can be:

• present tense: we use
• preterite: we used

So in isolation, it is ambiguous.

In this sentence, it will usually be understood as present because it sounds like a general habit or routine:

• Usamos el compostador para peladuras y posos de café.
  = We use the composter for peelings and coffee grounds.

If the context were clearly in the past, it could mean:

• Durante un tiempo, usamos el compostador...
  = For a while, we used the composter...

Here, para means for and shows purpose or use.

• usar algo para X = to use something for X

So:

• Usamos el compostador para peladuras y posos de café
  = We use the composter for peelings and coffee grounds

A native English speaker may expect something more like put into, but this sentence is about what the composter is used for, not the action of throwing things in.

If you wanted to focus on the action, Spanish might say:

• Echamos las peladuras y los posos de café en el compostador.
  = We put the peelings and coffee grounds in the composter.

Compostador means composter or compost bin.

In Spain, compostador is perfectly natural. You may also hear compostera in some places, but compostador is a very normal word.

So:

• el compostador = the composter / compost bin

The noun is masculine here, which is why it takes el.

El compostador suggests a specific, known composter — for example, the one at home, in the garden, or the one both speaker and listener already know about.

• Usamos el compostador... = We use the composter...
• Usamos un compostador... = We use a composter...

So el sounds more like our/the familiar one, while un would sound more indefinite.

Peladuras means peelings, parings, or the bits removed when peeling fruit or vegetables.

It is commonly used for things like:

• potato peelings
• carrot peelings
• apple peelings

A learner may compare it with:

• cáscaras = peels, shells, husks, outer coverings
• pieles = skins
• peladuras = specifically the pieces removed by peeling

In a compost context, peladuras is very natural.

Posos de café means coffee grounds, especially the used grounds left after making coffee.

This is different from:

• café molido = ground coffee in general, before or for brewing
• posos de café = the residue/grounds left over

So if you mean the stuff you throw into the compost after making coffee, posos de café is a very good choice.

Because Spanish usually talks about these things as plural mass-like items.

• peladuras = peelings, bits of peel
• posos = grounds / residue

Using the plural sounds natural when talking about kitchen scraps in general.

The singular forms exist, but they are less natural here:

• una peladura = one peeling / one strip of peel
• un poso = a deposit or sediment, often in other contexts

So the plural is the normal choice in this sentence.

Because Spanish often omits the article when talking about things in a general, non-specific way, especially after para.

So:

• para peladuras y posos de café = for peelings and coffee grounds in general

If you were talking about specific peelings and specific grounds, you might say:

• para las peladuras y los posos de café

But the version without articles sounds more general and very natural here.

It most naturally describes only posos.

So the structure is understood as:

• peladuras
• y posos de café

In other words:

• peelings
• and coffee grounds

It does not mean coffee peelings.

Yes, it is natural and correct, especially if you are describing what the composter is used for.

That said, in everyday speech, a Spanish speaker might also say:

• Echamos las peladuras y los posos de café en el compostador.
• Ponemos las peladuras y los posos de café en el compostador.

Those versions focus more on the action of putting things in.

So the difference is roughly:

• Usamos el compostador para... = talking about its purpose/use
• Echamos / ponemos ... en el compostador = talking about what we put into it