Luotettava kollega auttaa, kun on ongelma.

A simple breakdown is:

• luotettava = reliable / trustworthy
• kollega = colleague
• auttaa = helps
• kun = when
• on = is
• ongelma = problem

A very literal word-for-word version is:

• Reliable colleague helps, when is problem.

Natural English is:

• A reliable colleague helps when there is a problem.

Finnish has no articles, so there is no separate word for a/an/the.

So luotettava kollega can mean:

• a reliable colleague
• the reliable colleague
• sometimes a general idea like reliable colleagues

The exact meaning comes from context. In this sentence, English usually uses a reliable colleague or a generic a reliable colleague helps.

They are both in the nominative singular, because together they form the subject of the sentence.

Also, Finnish adjectives agree with the nouns they describe in:

• case
• number

So:

• luotettava kollega = both nominative singular

If the noun changed case or number, the adjective would change too.

In this sentence, you can safely treat luotettava as an adjective meaning reliable or trustworthy.

Morphologically, though, it comes from the verb luottaa = to trust, and it is a participial form. Its literal sense is something like:

• one that can be trusted

So in practice:

• luotettava ihminen = a trustworthy person
• luotettava kollega = a reliable colleague

Because the subject is singular:

• kollega = colleague

So the verb is in the 3rd person singular:

• auttaa = he/she/it helps

Finnish verbs show person and number, so you do not need a subject pronoun like he or she here.

Because Finnish does not use a dummy subject like English there in there is/there are.

English says:

• when there is a problem

Finnish says literally:

• when is a problem

This is normal Finnish. The noun ongelma comes after the verb in this kind of existential structure.

So kun on ongelma is a natural way to say:

• when there is a problem
• when a problem comes up

Here ongelma is in the nominative singular because the clause is affirmative and refers to a single countable thing:

• on ongelma = there is a problem

You often see the partitive in negative existential sentences:

• ei ole ongelmaa = there is no problem

So in this sentence:

• kun on ongelma = when there is a problem

is exactly what you would expect.

A very useful contrast is:

• kun = when
• jos = if

In this sentence, kun suggests a real or typical situation:

• Luotettava kollega auttaa, kun on ongelma.
• A reliable colleague helps when there is a problem.

If you used jos, it would sound more conditional:

• Luotettava kollega auttaa, jos on ongelma.
• A reliable colleague helps if there is a problem.

Both can be possible in some contexts, but kun is the more natural choice for when/whenever a problem occurs.

Most naturally, it means:

• when there is a problem

If you specifically want to say when someone has a problem, Finnish usually says who has it:

• kun sinulla on ongelma = when you have a problem
• kun jollakulla on ongelma = when someone has a problem

So without that extra word, kun on ongelma is best understood as a general there is a problem expression.

Because kun on ongelma is a subordinate clause, and standard Finnish separates subordinate clauses from main clauses with a comma.

So:

• Luotettava kollega auttaa, kun on ongelma.

This comma is normal and expected in written Finnish.

Yes. Finnish word order is fairly flexible.

For example, you could also say:

• Kun on ongelma, luotettava kollega auttaa.

This has the same basic meaning:

• When there is a problem, a reliable colleague helps.

The difference is mostly about emphasis and information flow:

• starting with luotettava kollega focuses first on the colleague
• starting with kun on ongelma focuses first on the situation

No, it does not have to name an object.

Here auttaa is used in a general sense:

• helps
• is helpful
• helps out

The sentence does not specify exactly whom the colleague helps. That is perfectly normal.

If you want to add the person being helped, you can:

• Luotettava kollega auttaa sinua. = A reliable colleague helps you.

Most naturally, it sounds like a general truth or habitual statement:

• A reliable colleague helps when there is a problem.

Finnish present tense is often used this way, just like English present tense in general statements.

So the sentence is not mainly about one single moment, but about what a reliable colleague typically does.