Teen lähtöselvityksen verkossa, jotta saan nousukortin ennen kuin menen lentokentälle.

Finnish often leaves out subject pronouns when they are obvious from the verb ending.

• teen = I do / I am doing
• the ending -n already tells you the subject is minä = I

So Teen lähtöselvityksen is a perfectly normal way to say I check in / I do the check-in. Adding minä would usually only be for emphasis or contrast.

Finnish uses the present tense very often for future meaning when the context makes the time clear.

In this sentence:

• Teen = I do / I will do
• saan = I get / I will get
• menen = I go / I will go

Because the sentence describes a plan and includes ennen kuin = before, Finnish does not need a separate future tense. This is very normal.

The basic noun is lähtöselvitys, which means check-in.

It is a compound word:

• lähtö = departure
• selvitys = clarification, processing, clearance

So the literal idea is something like departure processing, but in real usage it means check-in.

In the sentence, it appears as lähtöselvityksen because of object case.

Here lähtöselvityksen is the object of teen.

Finnish often uses the so-called total object when the action is seen as complete or as having a clear result. That is what happens here:

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

The -n ending is the normal singular total-object form in this type of sentence.

So the sentence is not talking about check-in as some vague ongoing activity; it is talking about completing one check-in.

Lähtöselvitystä would be the partitive form.

The partitive object is often used when the action is:

• incomplete
• ongoing
• indefinite
• part of something rather than the whole result

So compare:

• Teen lähtöselvityksen = I complete the check-in
• Teen lähtöselvitystä = I am doing check-in / I am working on the check-in

In your sentence, the idea is clearly a completed result, so lähtöselvityksen is the natural choice.

The base word is verkko, meaning net or network.

The ending -ssa is the inessive case, which often means in.

So:

• verkko = network / net
• verkossa = in the network, on the net, online

In natural English, verkossa here is simply online.

A very common alternative in everyday Finnish is netissä, which also means online / on the internet.

Jotta means so that or in order that.

It introduces a purpose clause: it explains why the speaker is doing the online check-in.

So:

• Teen lähtöselvityksen verkossa, jotta saan nousukortin...
• I check in online so that I get / can get the boarding pass...

It tells you the goal or purpose of the first action.

After jotta, Finnish normally just uses an ordinary finite verb.

So:

• jotta saan nousukortin = so that I get / can get the boarding pass

English often uses can in this kind of sentence, but Finnish does not always need a separate word like voin. The plain verb saan works naturally here and can carry that can get / manage to get sense from context.

The basic noun is nousukortti, meaning boarding pass.

It is another compound:

• nousu = boarding, rising, going up
• kortti = card

In the sentence, nousukortin is the object of saan:

• saan nousukortin = I get the boarding pass

It has -n for the same reason as lähtöselvityksen: it is a singular total object, referring to one complete item.

Ennen kuin means before when it is followed by a full clause.

So:

• ennen kuin menen lentokentälle = before I go to the airport

This structure is very common:

• ennen kuin lähden = before I leave
• ennen kuin syön = before I eat

Again, menen is present tense in form, but it can refer to the future.

The basic word is lentokenttä = airport.

Here it becomes lentokentälle, which is the allative case, often meaning to or onto a place.

• mennä lentokentälle = to go to the airport

This is the normal, idiomatic way to say it.

Finnish has several different location/direction cases, and they do not always match English exactly. In this expression, -lle is the standard choice for the destination. Even though in English we might imagine going into the airport, Finnish commonly says lentokentälle.

Yes, it is natural and correct.

It sounds like standard written or neutral spoken Finnish. A few everyday alternatives are also possible, for example:

• Teen lähtöselvityksen netissä...
• Tsekkaan itseni sisään netissä... (more colloquial, influenced by English)
• Teen check-inin netissä... (very colloquial, mixed style)

But your original sentence is clear, idiomatic, and good standard Finnish.