Learn Spanish (Latin America): La cena ya está preparada.

Here, está combined with the past participle preparada describes a resulting state. It means the action of preparing the dinner is finished, and we are now looking at the result: the dinner is ready. If we used es preparada, it would be the passive voice describing an action happening right now (for example, if you wanted to say 'Dinner is prepared by the chef every night').

Why does preparada end in -a?

When a past participle is used as an adjective with estar or ser, it must agree in gender and number with the noun it describes. Since la cena (the dinner) is feminine and singular, preparado changes to preparada.

Can I put ya at the end of the sentence instead?

Yes, you could say La cena está preparada ya. However, placing ya (already) right before the verb is the most natural and common word order in Spanish to emphasize that something is already done.

Could I use lista instead of preparada here?

Absolutely. La cena ya está lista means exactly the same thing. Preparada emphasizes that the meal was prepared by someone, while lista simply means it is ready, but they are practically interchangeable in this everyday context.