Refren tej piosenki jest łatwy.

Polish does not have articles like the or a/an. So Refren tej piosenki jest łatwy can naturally mean The chorus of this song is easy.

Polish usually lets context show whether something is definite or indefinite.

Because it means of this song, and in Polish that idea is usually expressed with the genitive case.

So:

• refren piosenki = the chorus of a song
• refren tej piosenki = the chorus of this song

After a noun like refren, the related noun often goes into the genitive to show possession or connection.

Tej is a form of the demonstrative ta = this / that for feminine nouns.

The base forms are:

• ten for masculine
• ta for feminine
• to for neuter

Since piosenka is a feminine noun, and here it is in the genitive singular, ta changes to tej.

So:

• ta piosenka = this song
• tej piosenki = of this song

Because piosenka is not the subject here. It is part of the phrase tej piosenki, which is in the genitive singular.

Dictionary form:

• piosenka = song

Genitive singular:

• piosenki = of a song

A useful thing to notice: piosenki can also be the nominative plural form, but here it is clearly genitive singular because it follows tej and means of this song.

Because łatwy is an adjective used after jest, and predicate adjectives in Polish normally stay in the nominative.

So:

• Refren jest łatwy. = The chorus is easy.

Compare that with predicate nouns, which are often instrumental:

• On jest nauczycielem. = He is a teacher.

So in this sentence, łatwy is correct because it is an adjective describing refren.

Because it has to agree with refren.

Refren is:

• masculine
• singular
• nominative

So the adjective also takes the masculine singular nominative form:

• łatwy

Compare:

• melodia jest łatwa = the melody is easy
• zadanie jest łatwe = the task is easy
• refren jest łatwy = the chorus is easy

Yes, in normal standard Polish, jest is needed here.

• Refren tej piosenki jest łatwy. = normal sentence

Leaving it out would sound incomplete in ordinary speech. Polish is not like Russian, where the present tense of to be is often omitted.

You may sometimes see omission in headlines, notes, or very informal shorthand, but not as the standard full sentence.

Yes. Polish word order is fairly flexible because the case endings show the grammatical relationships.

The most neutral order here is:

• Refren tej piosenki jest łatwy.

But you could also say:

• Tej piosenki refren jest łatwy.

That puts more emphasis on this song.

A more marked version would be:

• Łatwy jest refren tej piosenki.

That sounds more literary or contrastive, like It is the chorus of this song that is easy.

A rough English-friendly pronunciation is:

REF-ren tey pyo-SEN-kee yest WAT-vih

A more accurate IPA version is:

/ˈrɛ.frɛn tɛj pjɔˈsɛn.kʲi jɛst ˈwat.vɨ/

A few helpful notes:

• rz is not in this sentence, so no issue there
• j in Polish sounds like English y
• ł sounds like English w
• stress is usually on the second-to-last syllable

So:

• REF-ren
• pyo-SEN-ki
• ŁAT-wy

No. It is natural, but another very common Polish sentence would be:

• Ta piosenka ma łatwy refren.

Literally: This song has an easy chorus.

The difference is mostly in focus:

• Refren tej piosenki jest łatwy focuses on the chorus
• Ta piosenka ma łatwy refren focuses more on the song

Both are good Polish.