Turnu la karton.

Yes. Turnu is the -u form of the verb turni.

In Esperanto, -u is used for:

• commands
• requests
• instructions
• wishes / let-statements

So turnu here means something like Turn! or Turn it! / Turn the card! depending on context.

A very important beginner point:

• turni = the basic verb form, to turn
• turnu = turn!

So if you see -u, think of a command-like idea.

The -n marks the direct object in Esperanto.

Here:

• turnu = the action
• la karton = the thing being turned

So karton has:

• karto = card
• karton = card as the direct object

This is one of the most basic Esperanto grammar patterns:

• nouns normally end in -o
• direct objects add -n

So:

• la karto = the card
• turnu la karton = turn the card

English usually shows this by word order, but Esperanto often shows it with -n.

La is the definite article, meaning the.

So:

• karto = a card / card
• la karto = the card

In the sentence, la karton means the card as the object.

A useful thing to know: Esperanto has only one article here:

• la = the

It does not change for:

• singular/plural
• gender
• case by itself

The -n goes on the noun, not on la:

• la karto
• la karton
• la kartoj
• la kartojn

Because in Esperanto, commands often leave out the subject when it is understood.

So Turnu la karton. naturally means:

• Turn the card.
• understood subject: you

This is similar to English, where you usually do not say:

• You, turn the card.

You just say:

• Turn the card.

If you wanted to include the subject for emphasis, you could say:

• Vi turnu la karton.

But that is less neutral and usually adds emphasis or contrast.

Yes. The -u form is broader than just the English imperative.

It can also be used in sentences like:

• Li turnu la karton. = Let him turn the card.
• Ni turnu la karton. = Let’s turn the card.

But in your sentence, because there is no stated subject, the natural reading is a direct command:

• Turn the card.

So the form is technically more general, but here it works just like an imperative.

A simple learner-friendly pronunciation is:

TUR-nu la KAR-ton

Key points:

• Esperanto stress is almost always on the second-to-last syllable
• so:
  • TUR-nu
  • KAR-ton

Approximate vowel values:

• u sounds like oo in food
• a sounds like a in father
• o is a clear o sound, not a reduced English schwa

So:

• turnu ≈ TOOR-noo
• karton ≈ KAR-ton

No, not in standard Esperanto.

Because the card is the direct object of the verb turnu, it needs the accusative -n:

• correct: Turnu la karton.
• not correct: Turnu la karto.

Without -n, la karto would be just the basic noun form, not marked as the object.

In this sentence, it most naturally means something like:

• turn
• rotate
• flip over

With a card, English usually understands this as:

• turn the card over
• flip the card

The exact nuance depends on context:

• rotating it
• turning it around
• flipping it face-up or face-down

Esperanto turni covers that general idea of turning something.

The normal order here is very natural:

• Turnu la karton.

But because karton has the accusative -n, Esperanto word order is more flexible than English.

For example, you might also see:

• La karton turnu.

That is possible, but it is less neutral and usually gives special emphasis to the card.

For a beginner, the safest pattern is:

• verb + object
• Turnu la karton.

The dictionary forms are:

• turni = to turn
• la = the
• karto = card

In the sentence:

• turni becomes turnu
• karto becomes karton

So this sentence is a good example of how Esperanto changes words with predictable endings rather than many irregular forms.