El cubilete contiene el dado.

In Spain, cubilete usually means a dice cup: a small cup/container used to hold and shake dice.

Depending on context, cubilete can also mean a small container or holder, but with dado in the same sentence, the most natural reading is dice cup.

It is a masculine noun, so you say el cubilete.

Contiene is the 3rd person singular, present indicative form of contener:

• contener = to contain
• él / ella / usted contiene = he / she / it / you (formal) contains

So in El cubilete contiene el dado, the subject is el cubilete, and the verb agrees with it in the singular.

This verb is related to tener and has similar irregularities:

• yo contengo
• tú contienes
• él/ella contiene
• nosotros contenemos
• vosotros contenéis
• ellos contienen

Using el suggests we are talking about a specific cup and a specific die, or that both are already identifiable from the context.

So:

• El cubilete contiene el dado = The cup contains the die
• Un cubilete contiene un dado = A cup contains a die

The second version is grammatically fine, but it sounds more like you are introducing the objects for the first time, or speaking very generally.

No. In normal Spanish, singular count nouns usually need an article or another determiner.

So these are natural:

• El cubilete contiene el dado
• Un cubilete contiene un dado
• Este cubilete contiene ese dado

But Cubilete contiene dado sounds ungrammatical.

This is different from English, where article use is sometimes more flexible.

It is correct, but it can sound a bit formal, technical, or literal in everyday speech.

A native speaker in Spain might more naturally say:

• En el cubilete hay un dado. = There is a die in the cup.
• El cubilete tiene un dado dentro. = The cup has a die inside.
• El dado está en el cubilete. = The die is in the cup.

So contiene is fine, but not always the most conversational choice.

Yes. In Spanish:

• dado = die (singular)
• dados = dice (plural)

This is simpler than English, where the traditional singular is die and the plural is dice.

So:

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

Yes, absolutely.

Both sentences are correct, but they focus on slightly different things:

• El cubilete contiene el dado
  Focuses on the container and the idea of containing something.

• El dado está en el cubilete
  Focuses on the location of the die.

In many everyday situations, El dado está en el cubilete would sound more natural.

A helpful pronunciation guide is:

el koo-bee-LEH-teh kon-TYEH-neh el DAH-doh

Key points:

• cubilete → stress on -le-
• contiene → stress on -tie-
• dado → stress on da-

A few sound notes for Spain:

• c before u or o sounds like k
  so cu- and co- are hard k sounds
• the d in the middle of dado is softer than English d
• b and v are pronounced very similarly in Spanish

Because grammatical gender is a property of the noun itself.

• cubilete is masculine → el cubilete
• dado is masculine → el dado

With dado, the ending -o fits a very common masculine pattern.

With cubilete, the ending -e does not tell you automatically whether the noun is masculine or feminine, so you usually just learn it together with the article: el cubilete.

Grammatical gender here does not imply anything biological; these are just inanimate objects.

The normal, neutral order is:

• El cubilete contiene el dado.

That is the most straightforward way to say it.

You can change word order, but it usually changes the emphasis or sounds more marked:

• Dentro del cubilete está el dado.
  More emphasis on inside the cup
• El dado está en el cubilete.
  Focus on the die
• El dado lo contiene el cubilete.
  Grammatically possible, but much less natural in ordinary speech

So for a standard sentence, subject + verb + object is the best choice here.