Chci hodit kostkou.

• Chci = I want
• hodit = to throw / to toss / to roll
  In this context, it means to roll a die.
• kostkou = with a die / a die in the form required by this expression

So the structure is basically I want to roll a die.

Chci is the 1st person singular form of the verb chtít, which means to want.

The present-tense forms are irregular, for example:

• chci = I want
• chceš = you want
• chce = he/she/it wants

So Chci hodit kostkou literally means I want to throw/roll a die.

Czech often leaves out subject pronouns when they are already clear from the verb ending.

• Chci already means I want
• so já is not necessary

You could say Já chci hodit kostkou, but that usually adds emphasis, such as:

• I want to roll a die
• not someone else

The neutral, natural version is simply Chci hodit kostkou.

After chtít meaning to want, Czech normally uses an infinitive, just like English uses to + verb.

So:

• chci spát = I want to sleep
• chci jít = I want to go
• chci hodit kostkou = I want to roll a die

This is a very common pattern:

• chtít + infinitive

This is mainly about aspect, which is very important in Czech.

• hodit is perfective
• házet is imperfective

In simple terms:

• hodit = make one complete throw/roll
• házet = be throwing, throw repeatedly, or describe the activity in a more general way

So:

• Chci hodit kostkou = I want to make a roll / roll it once
• Chci házet kostkou = I want to be rolling dice / I want to throw a die repeatedly or as an activity

For a single intended action, hodit is the natural choice.

Because this expression uses the instrumental case.

The basic noun is:

• kostka = die / cube

Its instrumental singular is:

• kostkou

In the idiomatic expression hodit kostkou or házet kostkou, Czech uses the instrumental to mean roll a die.

This is something you mostly need to learn as a set phrase:

• hodit kostkou = to roll a die

Compare:

• hodit kostku would more likely mean throw the die as a physical object
• hodit kostkou means roll a die in the gaming sense

So the case changes the meaning.

Yes, kostka can mean several related things:

• cube
• block
• ice cube
• sugar cube
• die in the singular

The meaning depends on context.

In hodit kostkou, it clearly means a die because that is a standard expression for rolling a die.

A useful detail:

• singular: kostka = die
• plural: kostky = dice

In natural English, we usually say roll a die.

In Czech, the verb is hodit, which literally relates to throwing/tossing, but in this context it is the normal way to express rolling a die.

So:

• literal idea: throw/toss a die
• natural English translation: roll a die

This is a good example where the most natural translation is not always the most literal one.

Yes, Czech word order is flexible, but the neutral order here is:

• Chci hodit kostkou

Other orders are possible, but they change emphasis:

• Kostkou chci hodit = It is the die that I want to roll
• Hodit kostkou chci = more marked or poetic/emphatic

For normal everyday use, Chci hodit kostkou is the best choice.

Yes, you can.

Adding si often gives the sentence a slightly more natural, colloquial feeling, something like:

• I want to have a roll
• I want to roll a die for myself / just give it a roll

So:

• Chci hodit kostkou = fully correct
• Chci si hodit kostkou = also very natural, often a bit more conversational

The exact effect of si is subtle, so as a learner it is enough to know that both versions are possible.

It is not grammatically wrong, but it usually means something different.

• Chci hodit kostkou = I want to roll a die
• Chci hodit kostku = I want to throw the die

So with kostku in the accusative, the die is treated as the direct object being thrown somewhere. With kostkou in the instrumental, you get the usual gaming expression roll a die.

That is an important difference.

A simple learner-friendly approximation is:

• Chci ≈ kh-tsee
  The beginning is difficult for English speakers because of the consonant cluster chc-.
• hodit ≈ HO-dit
• kostkou ≈ KOST-koh

A few pronunciation tips:

• Czech stress is usually on the first syllable of each word
• ch in Czech is like the ch in German Bach or Scottish loch
• ou is a diphthong, roughly like oh + oo said smoothly together

So the rhythm is:

• CHCI HO-dit KOST-kou

Because Czech does not have articles.

So:

• kostka can mean a die or the die
• the exact meaning depends on context

In Chci hodit kostkou, English needs an article, so we say I want to roll a die, but Czech does not put anything there.

This is completely normal in Czech.