Ĉiu volontulo helpas dum du horoj.

Ĉiu is a correlatives word in Esperanto meaning each, every, or everyone, depending on what it refers to.

In Ĉiu volontulo helpas dum du horoj, ĉiu modifies the noun volontulo, so it means each volunteer or every volunteer.

A useful point:

• ĉiu volontulo = each/every volunteer
• ĉiuj volontuloj = all volunteers / every volunteer taken as a group

So this sentence focuses on each individual volunteer.

Because volontulo is the subject of the sentence, and subjects do not take the -n ending.

In Esperanto:

• the subject usually has no special ending
• the direct object takes -n

Here:

• Ĉiu volontulo = the subject, the person doing the helping
• helpas = helps

So volontulo stays in the basic noun form with -o.

The ending -as marks the present tense in Esperanto.

So:

• helpi = to help
• helpas = helps / is helping / does help
• helpis = helped
• helpos = will help

In this sentence, helpas simply tells us that the action happens in the present or as a general fact.

No, it does not have to state an object.

Esperanto often allows a verb like helpi to appear without saying exactly who or what is being helped, if that information is obvious, unknown, or unimportant.

So Ĉiu volontulo helpas dum du horoj means that each volunteer helps for two hours, without specifying whom they help.

If you wanted, you could add an object:

• Ĉiu volontulo helpas la infanojn dum du horoj. = Each volunteer helps the children for two hours.

Dum means during or for in the sense of duration.

In this sentence, dum du horoj means for two hours.

It tells us how long the helping lasts.

Examples:

• Mi laboris dum tri horoj. = I worked for three hours.
• Dum la kunveno mi silentis. = During the meeting I was silent.

So dum can introduce:

• a span of time: dum du horoj
• an event/time period: dum la tagmanĝo

Because after dum, the time expression is commonly used without the accusative -n.

So:

• dum du horoj = for two hours

This is the most straightforward form for expressing duration with dum.

You may also learn that Esperanto can express duration with the accusative alone:

• Mi laboris du horojn. = I worked two hours.

But in your sentence, the duration is introduced by dum, so du horoj is perfectly normal.

Yes. Esperanto can express duration in two common ways:

• Ĉiu volontulo helpas dum du horoj.
• Ĉiu volontulo helpas du horojn.

Both can mean Each volunteer helps for two hours.

The difference is mainly stylistic:

• dum du horoj explicitly uses a preposition
• du horojn uses the accusative of duration

Learners often find the dum version easier at first.

Because du means two, so the noun must be plural.

In Esperanto:

• singular nouns end in -o
• plural nouns end in -oj

So:

• horo = hour
• horoj = hours

That is why we say:

• unu horo = one hour
• du horoj = two hours

Yes, Esperanto word order is fairly flexible, because endings help show the grammatical roles.

The normal order here is:

• Ĉiu volontulo helpas dum du horoj.

But other orders are possible for emphasis, such as:

• Dum du horoj helpas ĉiu volontulo.
• Helpas ĉiu volontulo dum du horoj.

However, these sound more marked or literary. For most situations, the original order is the clearest and most natural.

A simple pronunciation guide is:

CHEE-oo vo-lon-TOO-lo hel-PAHS doom doo ho-ROY

A few details:

• ĉ sounds like ch in chair
• v is like English v
• j sounds like y in yes
• stress in Esperanto is always on the second-to-last syllable

So:

• Ĉiu → stress on the first syllable: ĈI-u
• volontulo → volonTUlo
• helpas → HELpas
• du → just du
• horoj → HOroj

Volontulo is a noun meaning volunteer.

It is built from:

• volont- = the root related to volunteering / willingness in this word family
• -ul- = a suffix meaning person characterized by
• -o = noun ending

So volontulo literally means something like a person of volunteering / a volunteer.

This is useful because Esperanto often builds words very regularly with roots and suffixes. Learning the parts helps you recognize and create new words more easily.