Kiam la signalo revenas, mia kolegino sendas al mi la dosieron tuj.

Kiam means when and introduces a time clause.

In this sentence, Kiam la signalo revenas sets the time for the main action:

• Kiam... = When...
• main clause = mia kolegino sendas al mi la dosieron tuj

So Esperanto is doing the same thing English does in a sentence like When the signal returns, my colleague sends me the file immediately.

The comma separates the introductory time clause from the main clause.

• Kiam la signalo revenas, = subordinate clause
• mia kolegino sendas al mi la dosieron tuj. = main clause

This is very common in Esperanto. When a clause like when, if, or because comes first, it is often followed by a comma.

Esperanto uses the present tense -as very broadly, including for:

• things that happen regularly
• general truths
• actions described in a neutral way without focusing on English-style tense differences

So revenas can mean:

• returns
• comes back
• sometimes even has come back, depending on context

Likewise, sendas is also present tense. The sentence may describe a habitual situation: whenever the signal comes back, the colleague sends the file right away.

Revenas comes from reveni, meaning to return or to come back.

It is made of:

• re- = back, again
• veni = to come

So la signalo revenas literally suggests the signal comes back or returns.

La is the definite article, meaning the.

So:

• la signalo = the signal
• signalo = a signal or just signal in a more general sense

The speaker is referring to a specific signal, not just any signal, so la is used.

Kolegino means female colleague.

It is built from:

• kolego = colleague
• -in- = female
• -o = noun ending

So:

• kolego = colleague / male colleague in traditional usage
• kolegino = female colleague

A learner may notice that Esperanto often uses -in- to mark female forms.

Because mia kolegino is the subject of the main verb sendas.

In Esperanto, the direct object usually gets -n, but the subject does not.

Here:

• mia kolegino = the person doing the sending, so it is the subject
• la dosieron = the thing being sent, so it is the direct object and gets -n

That is why:

• mia kolegino has no -n
• la dosieron does have -n

Because mi is the recipient, not the direct object.

• sendi ion al iu = to send something to someone

So:

• la dosieron = the thing being sent
• al mi = to me, the recipient

If you said sendas min, it would mean sends me, as if me were the thing being sent. That would be a completely different meaning.

Because prepositions normally do not require the accusative.

• al mi = to me
• por mi = for me
• kun mi = with me

The -n ending is mainly for direct objects and certain motion expressions. After al, you normally use the basic pronoun form, so mi, not min.

The -n marks the direct object.

The direct object is the thing directly affected by the verb. Here, what is being sent? The file.

So:

• la dosiero = the file
• la dosieron = the file as direct object

This is one of the most important features of Esperanto grammar.

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

For example, these would still be understandable:

• Kiam la signalo revenas, la dosieron mia kolegino sendas al mi tuj.
• Kiam la signalo revenas, tuj mia kolegino sendas al mi la dosieron.

But the original order is the most neutral and natural for many learners:

• time clause first
• then subject
• then verb
• then indirect object phrase
• then direct object
• then adverb

So even though word order can change, the given sentence is a good standard pattern.

Al specifically marks direction toward a person, often translated as to.

Compare:

• sendas al mi la dosieron = sends the file to me
• mi sendas la dosieron = I send the file

Without al, mi would not mean to me. The preposition is necessary to show the recipient clearly.

Tuj means immediately, right away, or at once.

Its position is fairly flexible. Putting it at the end is natural and easy:

• sendas al mi la dosieron tuj

It could also appear in other places for emphasis:

• mia kolegino tuj sendas al mi la dosieron
• mia kolegino sendas tuj al mi la dosieron

The version in your sentence sounds neutral and straightforward.

It could be either, depending on context, but many learners will naturally read it as a repeated or habitual action.

Because both verbs are in the present tense:

• Kiam la signalo revenas...
• ...mia kolegino sendas...

the sentence can mean something like:

• whenever the signal comes back, my colleague sends me the file right away

If the larger context were about a single event, it could also describe that event in a simple, neutral way.

Yes, very commonly.

A basic pattern is:

• sendi [thing] al [person]

So here:

• sendi la dosieron al mi = to send the file to me

This is similar to English send the file to me. Esperanto can express this very neatly with:

• direct object marked by -n
• recipient introduced by al

Esperanto is usually more regular and less tense-heavy than English.

English often distinguishes:

• when the signal returns
• when the signal has returned
• when the signal comes back

Esperanto often uses the simple present -as unless context demands something more specific:

• Kiam la signalo revenas

So learners should not expect Esperanto to match every English tense distinction exactly. Very often, the simple tense is enough.