Ili atendas la trajnon sur la perono.

Ili simply means they. Like English they, it does not show gender.

So Ili atendas... can mean:

• they are waiting...
• those people are waiting...

If you need to be more specific, you add extra words, but ili by itself is neutral.

In Esperanto, -as marks the present tense.

So:

• atendi = to wait
• atendas = waits / are waiting / is waiting

Esperanto uses the same present-tense form for both:

• They wait
• They are waiting

So Ili atendas can naturally mean They are waiting.

Because atendi works differently from English wait.

In Esperanto, atendi is usually directly transitive, so you say:

• atendi ion = to wait for something

That is why the sentence has:

• la trajnon = the train, as the direct object

So Esperanto says literally something like:

• They wait the train but in good English that means:
• They are waiting for the train

The -n ending marks the direct object.

Here, the thing being waited for is the train, so trajno becomes:

• trajnon

This is called the accusative ending.

Compare:

• la trajno alvenas = the train arrives
• ili atendas la trajnon = they are waiting for the train

Without -n, the grammar would be wrong here.

La is Esperanto’s definite article, meaning the.

It does not change for:

• singular or plural
• gender
• case

So it is always just la.

In this sentence:

• la trajnon = the train
• la perono = the platform

Even when the noun takes -n, la stays the same:

• la trajno
• la trajnon

Because this phrase describes location, not movement toward something.

• sur la perono = on the platform
• sur la peronon = onto the platform

In the sentence, they are already located there while waiting, so Esperanto uses:

• sur la perono

A very common rule is:

• no -n for a fixed location
• -n after a preposition if there is motion toward a place

Sur means on.

So:

• sur la perono = on the platform

That is the normal way to say someone is physically on the platform. Esperanto often uses prepositions in a fairly straightforward way here.

Depending on context, other prepositions exist, but sur is the natural choice for being on a platform surface.

Yes, Esperanto word order is fairly flexible, partly because the -n ending shows the direct object.

The normal order is:

• Ili atendas la trajnon sur la perono.

But you could also say:

• Sur la perono ili atendas la trajnon.
• La trajnon ili atendas sur la perono.

These all keep basically the same meaning, though the emphasis changes a little.

Still, for learners, the most natural default order is:

• subject + verb + object + other phrase

In normal use, sur la perono is understood as describing where they are waiting.

So the natural meaning is:

• They are waiting for the train on the platform.

Grammatically, prepositional phrases can sometimes attach in different ways, just as in English. But in real-life context, people usually wait on the platform, so that is the expected reading.

If someone wanted to make the train’s location especially clear, they might phrase it differently.

Because Esperanto usually does not need a special progressive form like English am waiting, are waiting, and so on.

The simple present often covers both:

• I wait
• I am waiting

So:

• Ili atendas can mean They wait or They are waiting

Esperanto does have participle forms, but they are not the normal first choice for an ordinary sentence like this.

The dictionary forms are:

• ili = they
• atendi = to wait for
• la = the
• trajno = train
• sur = on
• perono = platform

In the sentence, some words are changed by grammar:

• atendi → atendas because it is present tense
• trajno → trajnon because it is the direct object

Yes, perono normally means a platform, especially the kind at a train station.

So in this sentence:

• sur la perono strongly suggests a station platform

That also helps make the whole sentence feel natural:

• they are waiting for the train
• on the platform

Everything fits the usual railway context.