Kiam ni iris al la stacidomo, ekpluvis, do mi prenis la pluvombrelon.

Because the sentence is telling a past event. In Esperanto, the verb in the kiam-clause normally matches the time of the event being described.

• iris = went / were going
• iras = go / are going

So Kiam ni iris al la stacidomo... means When we went / were going to the station...

In storytelling, Esperanto often uses the simple past -is where English might use either went or were going, depending on context.

Ekpluvis means it started to rain or it suddenly began raining.

It is made from:

• pluvi = to rain
• ek- = a prefix meaning to begin or to start suddenly
• -is = past tense

So:

• pluvis = it rained / it was raining
• ekpluvis = it began to rain

The prefix ek- is very common in Esperanto for the start of an action:

• ekkuri = start running
• ekparoli = start speaking
• eksidi = sit down, start sitting

Because Esperanto does not use a dummy subject like English it in weather expressions.

English says:

• It is raining
• It rained

But Esperanto simply says:

• Pluvas
• Pluvis
• Ekpluvis

There is no need for a subject. The verb stands by itself.

Al means to or toward, so iri al la stacidomo means to go to the station.

• iri = to go
• al = to, toward
• la stacidomo = the station

This is the most straightforward way to show movement toward a place.

Esperanto can sometimes show direction with -n, but with iri, using al is extremely common and natural:

• Ni iris al la stacidomo = We went to the station

Stacidomo is a compound word:

• staci- = station-related root
• domo = house, building

So stacidomo literally means something like station building. In normal use, it means station, especially a railway station.

Compound words are very common in Esperanto, and learning to recognize their parts is very helpful.

Do means so, therefore, or thus.

It introduces a result or consequence:

• ekpluvis = it started to rain
• do mi prenis la pluvombrelon = so I took the umbrella

So do connects cause and result.

A useful comparison:

• ĉar = because
• do = therefore / so

For example:

• Ĉar ekpluvis, mi prenis la pluvombrelon.
• Ekpluvis, do mi prenis la pluvombrelon.

These are very close in meaning.

Because it is the direct object of prenis.

• mi prenis = I took
• What did I take? la pluvombrelon

In Esperanto, direct objects take the accusative ending -n.

So:

• la pluvombrelo = the umbrella
• mi prenis la pluvombrelon = I took the umbrella

This -n ending helps show clearly what receives the action.

La means the, so la pluvombrelon means the umbrella.

Esperanto uses la when the thing is specific or understood from the situation. Here, it suggests a particular umbrella, for example:

• the umbrella I had with me
• the umbrella we both know about
• the obvious umbrella needed because of the rain

If you said just pluvombrelon, it would sound more like an umbrella or some umbrella, depending on context.

Pluvombrelo is another compound word:

• pluvo = rain
• ombrelo = umbrella, parasol

So pluvombrelo literally means rain-umbrella, that is, an umbrella used for rain.

This is a nice example of how Esperanto builds vocabulary in a very logical way.

Yes, to some extent. Esperanto word order is fairly flexible because endings show grammatical function.

This sentence uses a very natural, neutral order:

• Kiam ni iris al la stacidomo, ekpluvis, do mi prenis la pluvombrelon.

You could rearrange parts for emphasis, but the original version is the most standard and easiest for learners.

For example, la pluvombrelon is clearly the object because of -n, even if moved. Still, Esperanto usually prefers a clear, simple order unless there is a reason to emphasize something.

The first comma separates the kiam-clause from the main clause:

• Kiam ni iris al la stacidomo, ...

That is similar to English punctuation after an opening when-clause.

The second comma before do helps separate the result phrase:

• ..., ekpluvis, do mi prenis...

This makes the structure easier to read:

1. Kiam ni iris al la stacidomo = time/background
2. ekpluvis = main event
3. do mi prenis la pluvombrelon = result

Basically when, but in context it can overlap a little with English while or as.

Kiam introduces a time clause. In this sentence, English could naturally say:

• When we went to the station...
• When we were going to the station...
• As we were going to the station...

So the exact English wording depends on context, but Esperanto simply uses kiam to mark the time relationship.