Kamizelka asekuracyjna poprawia bezpieczeństwo.

Because it is the subject of the sentence, so it is in the nominative case.

• kamizelka = vest
• asekuracyjna = safety / protective / buoyancy-related

The adjective asekuracyjna must match kamizelka in:

• gender: feminine
• number: singular
• case: nominative

That is why you get kamizelka asekuracyjna, not another ending.

Because kamizelka is a feminine singular noun, and the adjective has to agree with it.

In the nominative singular:

• masculine adjective often ends in -y / -i
• feminine adjective often ends in -a
• neuter adjective often ends in -e

So:

• asekuracyjny = masculine
• asekuracyjna = feminine
• asekuracyjne = neuter

Since kamizelka is feminine, the correct form is asekuracyjna.

Because poprawia is a conjugated present-tense verb, while poprawić is the infinitive.

• poprawia = improves / is improving
• poprawić = to improve

In a normal Polish sentence, you usually need a finite verb, so:

• Kamizelka asekuracyjna poprawia bezpieczeństwo. = correct
• Kamizelka asekuracyjna poprawić bezpieczeństwo. = incorrect

Also, poprawia comes from the imperfective verb poprawiać, which is often used for general statements like this one.

It is 3rd person singular, present tense.

That matches the singular subject kamizelka asekuracyjna.

So:

• ja poprawiam = I improve
• ty poprawiasz = you improve
• on/ona/ono poprawia = he/she/it improves

Here the subject is a thing, so in English we say it improves.

It is the direct object of poprawia, so it is in the accusative case.

However, bezpieczeństwo is a neuter singular noun, and for many neuter nouns the accusative form looks exactly the same as the nominative.

So:

• nominative: bezpieczeństwo
• accusative: bezpieczeństwo

Even though the form does not change, the function does: here it means safety as the thing being improved.

Normally, yes. Poprawiać is a transitive verb here, so the thing being improved goes into the accusative.

Examples:

• poprawia bezpieczeństwo = improves safety
• poprawia wyniki = improves results
• poprawia sytuację = improves the situation

So bezpieczeństwo is exactly where you would expect it after this verb.

Because Polish does not use articles like English does.

So kamizelka asekuracyjna can mean:

• a safety vest
• the safety vest

Which one is meant depends on the context.

In this sentence, the meaning is probably general:

• A safety vest improves safety

That kind of general statement is very common in Polish without any article.

Yes, Polish word order is more flexible than English because case endings show grammatical roles.

The neutral order here is:

• Kamizelka asekuracyjna poprawia bezpieczeństwo.

But you could also say:

• Bezpieczeństwo poprawia kamizelka asekuracyjna.
• Poprawia bezpieczeństwo kamizelka asekuracyjna.

These alternatives are grammatical, but they change the focus or emphasis.

The original sentence sounds the most natural as a simple, neutral statement.

A rough English-style guide is:

bez-pye-CHEN-stvo

A few useful details:

• pie in -pieczeń- sounds roughly like pye
• cz sounds like ch in chop
• ń is a soft n, a bit like the ny in canyon
• w in Polish sounds like English v

So bezpieczeństwo is approximately: bez-pye-CHEN-stvo

Not perfect, but close enough for a learner.

Not always exactly.

Kamizelka asekuracyjna usually refers to a buoyancy aid or safety vest used to help keep someone afloat and increase safety, especially in water sports.

A full life jacket is often:

• kamizelka ratunkowa

So the difference is often:

• kamizelka asekuracyjna = buoyancy aid / safety vest
• kamizelka ratunkowa = life jacket / rescue vest

In everyday use, though, people may sometimes translate both loosely as life jacket, depending on context.

Usually it sounds like a general truth or general statement:

• A safety vest improves safety.

Polish present tense can also describe something happening now, but in this sentence the most natural reading is general.

So poprawia here is best understood as:

• improves rather than
• is improving

Yes. That would also be very natural.

• poprawia bezpieczeństwo = improves safety
• zwiększa bezpieczeństwo = increases safety

Both work, but the nuance is slightly different:

• poprawia focuses on making something better
• zwiększa focuses on making the level of safety higher

In many contexts, both are good choices.