La baraja, la carta y el dado están listos.

In this sentence:

• la baraja = the deck (of cards)
• la carta = the card
• el dado = the die

A useful note: in everyday English, people often say dice even for one item, but in careful English, one is a die and more than one are dice.

Spanish often uses the definite article more explicitly than English does. Here, each item is presented as its own specific thing:

• la baraja
• la carta
• el dado

So Spanish naturally repeats the article. In English, we might also say the deck, the card, and the die.

Because the subject is plural overall. Even though each noun is singular by itself, together they form a compound subject:

• la baraja
• la carta
• y el dado

That means the deck + the card + the die = they, so the verb must be plural:

• están listos = are ready

If there were only one thing, you would use está:

• La baraja está lista.

Because the group includes at least one masculine noun: el dado.

In Spanish, when a group has:

• all feminine nouns → adjective is usually feminine plural
• at least one masculine noun → adjective is usually masculine plural

Here:

• la baraja = feminine
• la carta = feminine
• el dado = masculine

So the mixed group takes masculine plural:

• están listos

If all three nouns were feminine, you would say listas.

Because estar is used for a condition or state, and ready is treated as a temporary state.

• estar listo = to be ready
• ser listo can mean to be clever/smart, especially in many varieties of Spanish

So:

• están listos = they are ready
• son listos could sound like they are clever

That is a very important difference.

Yes. Carta can also mean letter. Spanish words often have more than one meaning depending on context.

Here, because the sentence also has baraja and dado, the context strongly suggests games or playing cards, so carta is understood as card, not letter.

Baraja and carta are related, but they are not the same thing:

• baraja = deck of cards
• carta = one card

So a baraja is made up of many cartas.

Yes. Dado is the standard word for die.

Forms:

• el dado = the die
• los dados = the dice

This is a very common word in games and board-game vocabulary.

Yes, you could say La baraja, la carta y el dado están preparados, and it would be understandable.

But listos is the more natural everyday choice for ready in a sentence like this. Preparados can sound a bit more like prepared than ready.

So:

• están listos = more natural for are ready
• están preparados = also possible, but slightly different in tone

The accent mark in están shows the stress pattern and distinguishes the form clearly in writing.

This is the they/you all form of estar in the present tense:

• yo estoy
• tú estás
• él/ella está
• nosotros estamos
• ustedes/ellos/ellas están

So the accent is simply part of the correct spelling of that verb form.