Jak tylko ktoś wywróci się, użyj rzutki ratowniczej.

It is a fixed expression meaning as soon as.

Do not translate it word for word as how only. In Polish, jak tylko often introduces something that should happen immediately after another event.

A close alternative is gdy tylko, which also means as soon as.

Because this sentence is talking about one future completed event.

• wywróci się = from the perfective verb wywrócić się
• perfective verbs in Polish use present-looking forms to talk about the future

So ktoś wywróci się means someone will fall over / capsize.

By contrast:

• wywraca się is imperfective
• it suggests a repeated, ongoing, or habitual action

Here, the sentence means when that one event happens, do this immediately, so the perfective form is the natural choice.

Here się is part of the verb wywrócić się.

Compare:

• wywrócić coś = to overturn something
• wywrócić się = to overturn / fall over / capsize

So się changes the verb from acting on something else to describing what happens to the subject itself.

It is not always best translated as oneself in English. Very often, as here, it is just a normal part of the Polish verb.

użyj is the imperative form of użyć, so it means use!

This form is used for a direct instruction to one person.

In this kind of safety instruction, Polish naturally uses the imperative:

• użyj = use
• zrób = do
• weź = take

If you were speaking to more than one person, you would say użyjcie.

This is an aspect question.

• użyć is perfective
• używać is imperfective

So:

• użyj means use it now / use it once / perform the action
• używaj means more like use it regularly, keep using it, or be using it

In an emergency instruction, Polish normally prefers the perfective imperative, because it points to a single concrete action.

Because the verb użyć takes the genitive case, not the accusative.

The dictionary form is:

• rzutka ratownicza

But after użyć, it becomes:

• rzutki ratowniczej

So the sentence literally follows the pattern:

• użyć + genitive

This is something learners often just have to memorize, because some Polish verbs require a case that does not match what English would use.

The basic form is rzutka ratownicza.

Here is the change:

• nominative singular: rzutka ratownicza
• genitive singular: rzutki ratowniczej

Both words change because the adjective must agree with the noun in:

• gender
• number
• case

Since rzutka is feminine singular, the adjective ratownicza changes with it.

In this context, it means a rescue throw line or throw bag used in water rescue.

That matters because rzutka can look confusing to learners. In other contexts, similar-looking words may suggest something like a throw or even a dart, but here the rescue context makes the meaning specific: it is rescue equipment.

No, Polish word order is fairly flexible.

You can also hear:

• ktoś się wywróci

Both are possible. The version in your sentence is natural and clear.

A useful thing to remember is that się usually does not go at the very beginning of a clause, but otherwise its position can move around depending on rhythm, emphasis, and style.

Because Jak tylko ktoś wywróci się is a subordinate clause placed before the main clause.

So Polish writes:

• Jak tylko ktoś wywróci się, użyj rzutki ratowniczej.

This is the normal punctuation pattern when the as soon as... clause comes first.