Mi havas nur unu demandon.

In Esperanto, verbs do not change according to the subject. The ending -as always marks the present tense.

So:

• mi havas = I have
• vi havas = you have
• li havas = he has
• ili havas = they have

This is much simpler than English, where we say I have but he has.

Nur means only or just.

In Mi havas nur unu demandon, it limits unu demandon, so the meaning is I have only one question.

Esperanto word order is flexible, but here nur naturally goes before the thing it limits:

• nur unu demandon = only one question

Unu is the normal Esperanto word for one.

It can work as:

• a number: unu, du, tri...
• something close to an adjective before a noun: unu demando = one question

In this sentence, unu tells us the quantity of demandon.

The -n ending marks the direct object in Esperanto.

In this sentence:

• Mi = the subject, the one doing the action
• havas = have
• demandon = the thing being had

So demando becomes demandon because it is the direct object of havas.

This is one of the most important grammar rules in Esperanto.

Only the noun must have the -n ending here, so:

• unu demando = one question
• unu demandon = one question, as a direct object

Since unu is not taking an -j or -n ending here, it stays unu.

Compare that with regular adjectives, which do match the noun:

• bona demando
• bonan demandon

But with unu, you normally just keep unu.

Esperanto has no indefinite article like English a/an.

So:

• demando can mean a question or just question, depending on context.

Esperanto does have a definite article, la, for the, but it is not used here because the sentence means something like I have only one question, not I have only the one question.

Yes, Esperanto allows fairly flexible word order, especially because the -n ending helps show what the object is.

The normal order here is:

• Mi havas nur unu demandon.

But other orders are possible for emphasis, such as:

• Nur unu demandon mi havas.

That said, the original sentence is the most neutral and natural for beginners to use.

A simple pronunciation guide is:

• Mi ≈ mee
• havas ≈ HAH-vahs
• nur ≈ noor
• unu ≈ OO-noo
• demandon ≈ deh-MAHN-don

A few helpful points:

• Esperanto pronunciation is very regular.
• Stress is usually on the second-to-last syllable.
• So you get: HA-vas, U-nu, de-MAN-don.

Yes. Demando is the standard Esperanto word for question.

Related forms include:

• demandi = to ask
• demando = question

So you can often see the connection between verbs and nouns clearly in Esperanto.

Yes, in many contexts it can.

Because nur can often be translated as only or just, English may render the sentence as:

• I have only one question
• I just have one question

The exact best translation depends on tone and context, but the Esperanto structure itself is straightforward: it says the speaker has one question and no more than one.