Jos teen lähtöselvityksen myöhässä, lento voi lähteä ilman minua.

Jos means if. It introduces a condition:

• Jos teen lähtöselvityksen myöhässä = If I check in late

So the sentence has the typical if-clause + result-clause structure:

• Jos ... , ...
• If ... , ...

In Finnish, this is very common and works much like English.

Finnish usually uses the present tense for both present and future meaning when the context is clear.

So:

• Jos teen ... literally looks like If I do ...
• but in context it can mean If I do / if I end up doing / if I check in late

Likewise:

• lento voi lähteä = the flight may leave

Even if this is about a future flight, Finnish normally does not need a separate future tense.

Finnish often leaves out subject pronouns when the verb ending already shows who the subject is.

• teen = I do
• the ending -n tells you the subject is I

So:

• teen already means I do
• minä teen is also possible, but more emphatic

In neutral everyday Finnish, dropping minä is very common.

Lähtöselvitys means check-in, especially for travel, airports, and flights.

It is built from:

• lähtö = departure
• selvitys = clarification, processing, formal handling

Together, lähtöselvitys is the standard Finnish word for check-in.

So:

• tehdä lähtöselvitys = to check in
• tehdä lähtöselvityksen = to do the check-in

Because it is the object of teen.

The basic form is:

• lähtöselvitys = check-in

Here it becomes:

• lähtöselvityksen

This -n form is very common for a total object: the action is seen as completed or as a whole.

So:

• teen lähtöselvityksen = I do the check-in / I complete the check-in

A learner may notice that this form looks like the genitive, and historically it is related, but in sentences like this it is best understood as the normal object form used for a completed whole action.

Because myöhässä means late in the sense of being late, while myöhään means late in the sense of at a late time.

Compare:

• Olen myöhässä = I am late
• Tulin myöhään = I came late / at a late hour

In your sentence:

• teen lähtöselvityksen myöhässä

the meaning is I do the check-in late / too late / when I am late, so myöhässä is the natural choice.

A useful shortcut:

• myöhässä = late, behind schedule
• myöhään = late in time, late at night, at a late point

Here voi means something like can or may, expressing possibility.

• lento voi lähteä ilman minua = the flight can/may leave without me

In natural English, may or could often matches the meaning better than a literal can.

The verb is:

• voida = can, be able to, may

Here it does not mean permission. It means it is possible that.

Because modal verbs in Finnish are followed by the basic infinitive.

• voi lähteä = can/may leave
• haluan mennä = I want to go
• saan tulla = I may come / I get to come

So:

• voi is the finite verb
• lähteä stays in the infinitive

This is very similar to English:

• may leave
• can go

not may leaves or can goes

Because ilman requires the partitive case.

• minä = I
• minut = me
• minua = me, in the partitive

So:

• ilman minua = without me

This is something you mostly just learn as a pattern:

• ilman rahaa = without money
• ilman takkia = without a coat
• ilman minua = without me

So after ilman, expect the next word to be in the partitive.

Because Finnish normally uses a comma between the jos-clause and the main clause.

• Jos teen lähtöselvityksen myöhässä, lento voi lähteä ilman minua.

This is standard punctuation, much like English often writes:

• If I check in late, the flight may leave without me.

If the order is reversed, Finnish often still uses a comma:

• Lento voi lähteä ilman minua, jos teen lähtöselvityksen myöhässä.

Yes. Finnish word order is fairly flexible, although some versions sound more natural in certain contexts.

The neutral version is:

• Jos teen lähtöselvityksen myöhässä, lento voi lähteä ilman minua.

You could also say:

• Lento voi lähteä ilman minua, jos teen lähtöselvityksen myöhässä.

Both are correct. The difference is mainly about focus:

• starting with Jos... puts the condition first
• starting with Lento voi lähteä... puts the result first

It usually sounds like a real, practical possibility.

Finnish uses the present tense in jos clauses for normal real conditions:

• Jos teen ... , lento voi lähteä ...
• If I check in late, the flight may leave ...

This is not especially remote or imaginary. It is more like a warning about what can happen in real life.

If Finnish wanted to sound more clearly hypothetical or unlikely, it might use the conditional in some contexts, but this sentence as written is the normal way to talk about a real possible consequence.

Yes. Lento means flight, that is, the scheduled air journey.

So:

• lento lähtee = the flight leaves / departs

In everyday language, this can refer to the trip or service, even though of course the airplane is physically the thing that departs. This is just like English:

• My flight leaves at six.

Yes, very often that is the practical implication.

The sentence literally says late, but in airport context the idea is often:

• If I check in too late, the flight may leave without me

So the exact nuance depends on context:

• myöhässä = late
• in many real-life situations, it effectively means too late to avoid problems

That is why the second clause makes sense: being late with check-in can cause you to miss the flight.