Tira el dau.

Because this is a command.

• tires = you roll / you throw (statement, present tense)
• tira = roll / throw! (informal singular command)

With many -ar verbs in Catalan, the tu imperative has the same form as the 3rd person singular present:

• tirar → tira

So:

• Tu tires el dau. = You roll the die.
• Tira el dau. = Roll the die.

It is the informal singular imperative of tirar.

That means you use it when speaking to one person you would address as tu.

The infinitive is:

• tirar = to throw, to toss, to roll

In this sentence, tira means something like roll!

el is the masculine singular definite article, meaning the.

So:

• el dau = the die

Catalan uses articles very regularly, and here dau is a singular masculine noun, so el is the correct article.

Strictly speaking, dau means one die.

Its plural is:

• daus = dice

So:

• el dau = the die
• els daus = the dice

This is actually clearer than everyday English, where people often say dice for both singular and plural.

Yes. In Catalan, tirar is the usual verb in this context.

Literally, tirar can mean things like:

• to throw
• to toss
• to cast

But with a die, it naturally corresponds to English to roll:

• Tira el dau. = Roll the die.
• Tira els daus. = Roll the dice.

So even if the core idea is throw/cast, in game situations roll is the best English equivalent.

Because Catalan often omits subject pronouns when they are understood from the verb form or the situation.

So:

• Tira el dau. is completely normal.
• Tu tira el dau. is generally unnecessary and sounds marked.

If you do include tu, it is usually for emphasis, contrast, or clarification:

• Tu, tira el dau; jo escriuré els punts.
  = You roll the die; I’ll write down the points.

In ordinary commands, just the verb is enough.

That depends on who you are speaking to.

• Tira el dau. = informal, to one person (tu)
• Tiri el dau. = formal, to one person (vostè)
• Tireu el dau. = informal, to more than one person (vosaltres)
• Tirin el dau. = formal, to more than one person (vostès)

So tira is specifically the form for giving the command to one person informally.

A good approximate pronunciation is:

• TEE-ruh el DOW

A bit more precisely:

• tira → TEE-ra or TEE-rə, depending on accent
• el → el or a weaker uhl
• dau → rhymes roughly with English now

Notes:

• The r in tira is a light tapped r, not a heavy English r
• au in dau sounds like the vowel in now

Pronunciation varies by dialect, but that approximation will be understood.

Yes, absolutely.

You can write:

• Tira el dau.
• Tira el dau!

Both are possible. The version with ! makes the command feel more obviously forceful, energetic, or game-like.

In instructions, Catalan often uses either punctuation style depending on tone and context.