La ĉeno estas sur la dentrado.

La is the Esperanto definite article, meaning the.

So:

• la ĉeno = the chain
• la dentrado = the gear / the sprocket / the cogwheel

Esperanto has only one definite article: la. It does not change for gender, number, or case in normal use.

Estas means is / are / am.

It is the present-tense form of the verb esti = to be.

So:

• La ĉeno estas sur la dentrado. = The chain is on the gear.

Esperanto verbs do not change depending on the subject:

• mi estas = I am
• vi estas = you are
• li estas = he is
• ili estas = they are

So estas always stays the same in the present tense.

Because la dentrado is not the direct object here.

In Esperanto, the -n ending is often used for the direct object, but in this sentence we have:

• La ĉeno = the subject
• estas = is
• sur la dentrado = a prepositional phrase meaning on the gear

After the preposition sur (on), you normally do not add -n when you mean location.

So:

• sur la dentrado = on the gear

If you were talking about movement onto something, Esperanto can sometimes use -n:

• sur la dentradon = onto the gear

But this sentence describes a position, not movement.

Sur means on.

It is a preposition showing position or contact with a surface.

Examples:

• sur la tablo = on the table
• sur la muro = on the wall
• sur la dentrado = on the gear

In this sentence, it tells you where the chain is located.

A simple pronunciation guide:

• ĉ is pronounced like ch in chair
• e is like e in bet
• o is like a clear o
• a is like a in father

So:

• ĉeno sounds roughly like CHEH-no
• dentrado sounds roughly like den-TRAH-do

Also, Esperanto usually stresses the second-to-last syllable:

• ĈE-no
• den-TRA-do

Ĉeno usually means chain, and it works much like the English word.

It can refer to:

• a physical chain made of links
• a bicycle chain
• sometimes a figurative chain, depending on context

In this sentence, it most likely refers to a mechanical chain, such as a bicycle or machine chain.

Dentrado is a compound word.

It can be understood as:

• dent- = tooth
• rad- = wheel
• -o = noun ending

So dentrado literally means something like toothed wheel.

That is why it can mean:

• gear
• cogwheel
• sprocket

Esperanto often builds words this way, by combining meaningful parts.

Yes, the word order can sometimes be changed, but this order is the most neutral and natural.

The basic structure is:

• La ĉeno = subject
• estas = verb
• sur la dentrado = location

So it follows a very familiar pattern for English speakers:

The chain + is + on the gear

You could change the order for emphasis, for example:

• Sur la dentrado estas la ĉeno.

But that is less neutral and more marked. For a learner, the original sentence is the standard way to say it.

Because -o is the standard noun ending in Esperanto.

So:

• ĉen-o = chain
• dentrad-o = gear

This is one of the most regular features of Esperanto. If you see a word ending in -o, it is a noun.

Other common endings are:

• -a = adjective
• -e = adverb
• -i = infinitive verb

Normally, no. Esperanto keeps la unchanged.

So you say:

• la ĉeno
• la dentrado
• la avo
• la amiko

In poetry or very special style, you may sometimes see l’, but learners should usually just use la.

Yes. Depending on context, dentrado may be translated as:

• gear
• cogwheel
• toothed wheel
• sprocket

In a sentence with ĉeno (chain), sprocket may be especially natural in some contexts, such as bicycles or machinery.

So the exact English word can vary, even though the Esperanto sentence stays the same.