La denuncia ya está firmada.

La is the feminine singular definite article, meaning the.

Spanish often uses the article where English might also use the:

• la denuncia = the complaint / the report

You could sometimes omit the article in other contexts, but in this sentence la denuncia refers to a specific document or complaint that both speakers know about.

In Spain, denuncia usually means a formal complaint or report, often a legal or police one.

Depending on context, it can mean:

• a police report
• a formal complaint
• an official accusation/report of wrongdoing

So it is usually more formal than just a casual complaint.

Ya often means already.

So:

• La denuncia está firmada = The complaint/report is signed
• La denuncia ya está firmada = The complaint/report is already signed

It adds the idea that the action has been completed, often earlier than expected or by now.

Common uses of ya:

• Ya viene. = He/She is coming now / already on the way.
• Ya lo sé. = I already know.

Because estar + past participle is used here to describe a resulting state.

• está firmada = is signed / has been signed in the sense of it is now in a signed state

This is different from ser, which is used for:

1. essential characteristics
2. the true passive with focus on the action

Compare:

• La denuncia está firmada. = The report is signed.
  
  • focus: its current condition
• La denuncia fue firmada por el abogado. = The report was signed by the lawyer.
  
  • focus: the action/event

So in your sentence, the idea is the current status of the document.

Because firmada agrees with denuncia, which is a feminine singular noun.

Agreement works like this:

• el documento está firmado
• la denuncia está firmada
• los documentos están firmados
• las denuncias están firmadas

The participle acts a bit like an adjective here, so it changes to match the noun.

It is originally the past participle of firmar (to sign), but in this sentence it functions very much like an adjective describing the state of the noun.

So grammatically:

• firmada = past participle of firmar
• in está firmada, it describes the present condition of la denuncia

That is why it agrees in gender and number.

It is closer to a resultative construction than to a standard passive.

• La denuncia ya está firmada.
  Focuses on the result: the complaint is now signed.

A more clearly passive sentence would be:

• La denuncia ya ha sido firmada. = The complaint has already been signed.

Both can translate similarly in English, but Spanish often prefers estar + participle when talking about the resulting state rather than the action itself.

Yes, but it means something slightly different in focus.

• La denuncia ya está firmada.
  Focus on the current state: it is now signed.

• La denuncia ya se ha firmado.
  Focus more on the completed action: it has now been signed.

So both are possible, but your original sentence sounds very natural when someone is checking whether the document is ready.

Spanish often leaves that out if it is unknown, obvious, or unimportant.

This sentence only tells us the state of the document, not the person who signed it.

If you want to add the person, you would usually switch structure:

• La denuncia ya está firmada por el denunciante.
• La denuncia ya ha sido firmada por el abogado.

But if the important information is simply that the signature is done, leaving out the agent is very natural.

The accent distinguishes está (from the verb estar) from esta (this, feminine).

Compare:

• está = is
• esta denuncia = this complaint/report

So:

• La denuncia ya está firmada. = The report is already signed.
• Esta denuncia... = This complaint/report...

The accent helps show they are different words.

Yes, a little.

The most neutral order is:

• La denuncia ya está firmada.

You may also hear:

• La denuncia está ya firmada.

This is possible, but less neutral in many contexts.
For most learners, ya before the verb is the safest and most natural choice:

• ya está

Spanish word order is somewhat flexible, but not completely free. The original sentence is the best standard version to learn first.