W szkole mieliśmy krótkie szkolenie, jak ratować kogoś, zanim przyjedzie karetka.

Because szkoła normally takes the preposition w when you mean in/at school as a location.

• w szkole = in/at school
• The noun szkoła changes to szkole because w requires the locative case here.

So:

• szkoła → basic form
• w szkole → at school / in school

For a native English speaker, it helps to learn this as a set phrase: w szkole.

In Polish, the subject pronoun is often omitted because the verb ending already shows who is doing the action.

• mieliśmy = we had
• the ending -śmy tells you it is we

So Polish often says:

• Mieliśmy krótkie szkolenie
  rather than
• My mieliśmy krótkie szkolenie

Adding my is possible, but it usually gives extra emphasis, like we in contrast to someone else.

Yes. Mieliśmy is literally we had, from the verb mieć = to have.

But in Polish, mieć szkolenie is a very natural way to say:

• to have training
• to attend a training session
• to undergo training

So mieliśmy krótkie szkolenie is not strange Polish at all. It is a normal expression.

Because szkolenie is a neuter singular noun, and krótkie has to match it.

• szkolenie = training session / training course
• it is neuter
• so the adjective must also be in the neuter singular form: krótkie

Here, krótkie szkolenie is the object of mieliśmy. With this kind of noun, the accusative singular looks the same as the nominative singular, so the form stays krótkie szkolenie.

Close, but not exactly in how it behaves grammatically.

In English, training is often uncountable:

• We had some training

In Polish, szkolenie is a normal countable noun:

• mieliśmy szkolenie = we had a training session
• dwa szkolenia = two training sessions

So in this sentence, szkolenie sounds like a specific session or course, not just the abstract idea of training.

This is a very common Polish pattern:

• jak + infinitive

It means how to do something.

So:

• jak ratować kogoś = how to save/help someone
• literally: how to rescue someone

Other examples:

• jak gotować = how to cook
• jak się uczyć = how to study
• jak otworzyć drzwi = how to open the door

So jak here does not mean like. It means how.

This is about aspect, which is very important in Polish.

• ratować = imperfective
• uratować = perfective

Very roughly:

• ratować focuses on the process, the actions, the attempt
• uratować focuses on a completed successful result

In this sentence, jak ratować kogoś sounds natural because a training session teaches the procedure: what to do, how to act, how to help until the ambulance arrives.

If you said jak uratować kogoś, it would sound more like how to save someone successfully / how to rescue someone completely, which is less natural in this first-aid context.

Kogoś is the pronoun someone in the form needed after ratować.

• dictionary form: ktoś = someone
• after ratować, you need the accusative
• the accusative form is kogoś

So:

• ratować kogoś = to save/help someone

This is a useful pair to remember:

• ktoś = someone
• kogoś = someone (as an object)

Because Polish punctuation usually separates subordinate clauses more consistently than English does.

Here you have:

• main clause: W szkole mieliśmy krótkie szkolenie
• subordinate clause: jak ratować kogoś
• another subordinate clause: zanim przyjedzie karetka

So the commas help divide those parts.

In Polish, commas before words like jak, że, bo, kiedy, zanim are very common when they introduce clauses.

It looks present, but with a perfective verb like przyjechać, those forms usually refer to the future.

• przyjechać = perfective, to arrive
• przyjedzie = will arrive

So:

• zanim przyjedzie karetka = before the ambulance arrives / will arrive

This is a key Polish pattern:

• imperfective present form = present time
• perfective present-looking form = future meaning

That is just word order. Polish word order is more flexible than English.

This clause could also be:

• zanim karetka przyjedzie

Both are understandable, but zanim przyjedzie karetka sounds very natural.

Putting karetka after the verb can make the clause flow a bit more smoothly and can keep the focus on the event of the ambulance arriving.

Usually karetka means ambulance, especially the vehicle.

In many contexts, though, English also says before the ambulance arrives, even though the real meaning includes the medical team. Polish works similarly here.

So in this sentence, karetka naturally means the ambulance / the ambulance crew coming to the scene.

Yes. That is also correct.

Polish word order is flexible, and changing it often changes emphasis rather than basic meaning.

Compare:

• W szkole mieliśmy krótkie szkolenie
  emphasis starts with at school
• Mieliśmy w szkole krótkie szkolenie
  emphasis starts more with we had
• Krótkie szkolenie mieliśmy w szkole
  more marked, possible in the right context

So the original sentence is natural, but it is not the only possible order.

Yes, that is the natural interpretation.

The phrase:

• jak ratować kogoś, zanim przyjedzie karetka

strongly suggests emergency help before professional medical help arrives, so it sounds like first-aid training.

A more explicit version could be:

• mieliśmy krótkie szkolenie z pierwszej pomocy = we had a short first-aid training session

But the original sentence is still completely natural and clear.