Mój współlokator jest cichy, a nowa współlokatorka lubi słuchać muzyki wieczorem.

Mój means my.

It agrees with the noun współlokator (male roommate / flatmate), which is:

• masculine
• singular
• nominative case, because it is the subject of the sentence

So:

• mój współlokator = my male roommate

If the noun were feminine, you would use a different form:

• moja współlokatorka = my female roommate

Polish possessive words like my, your, our change form to match the noun they describe.

They both refer to a person you live with, but the difference is gender:

• współlokator = a male roommate / flatmate
• współlokatorka = a female roommate / flatmate

This is very common in Polish. Many nouns have:

• a masculine form
• a feminine form

Here, the sentence mentions one male roommate and one female roommate:

• Mój współlokator
• nowa współlokatorka

Because cichy must agree with współlokator.

In Polish, adjectives change depending on the noun’s:

• gender
• number
• case

Here:

• współlokator is masculine singular
• so the adjective is cichy

Compare:

• współlokator jest cichy = the male roommate is quiet
• współlokatorka jest cicha = the female roommate is quiet

So cichy is simply the masculine singular form of quiet.

Because nowa (new) must match współlokatorka.

Since współlokatorka is:

• feminine
• singular
• nominative

the adjective also takes the feminine singular nominative form:

• nowy = masculine
• nowa = feminine
• nowe = neuter

So:

• nowy współlokator = new male roommate
• nowa współlokatorka = new female roommate

This is a very common Polish pattern.

• lubi = likes
• słuchać = to listen

So lubi słuchać literally means likes to listen.

After verbs like lubić (to like), Polish often uses the infinitive of the second verb:

• lubi czytać = likes to read
• lubi pływać = likes to swim
• lubi słuchać muzyki = likes to listen to music

So the structure is very similar to English:

• likes to listen

Because the verb słuchać requires the genitive case.

The basic form is:

• muzyka = music

But after słuchać (to listen to), the noun changes:

• słuchać muzyki = to listen to music

This is something learners often just have to memorize:

• słuchać muzyki = listen to music
• słuchać radia = listen to the radio
• słuchać nauczyciela = listen to the teacher

So muzyki is the genitive singular form of muzyka.

Wieczorem means in the evening or at night / in the evening, depending on context.

It comes from wieczór (evening), but here it appears in the instrumental case:

• wieczór = evening
• wieczorem = in the evening

This is a common Polish time expression. Some parts of the day are often used in special case forms:

• rano = in the morning
• wieczorem = in the evening
• nocą = at night / during the night

So in this sentence:

• lubi słuchać muzyki wieczorem = she likes listening to music in the evening

Both a and i can connect parts of a sentence, but they are not used in exactly the same way.

• i usually means and, simply joining things
• a often means and / whereas / while, showing a contrast or a shift

In this sentence:

• Mój współlokator jest cichy, a nowa współlokatorka lubi słuchać muzyki wieczorem.

The speaker is not just listing two facts. There is a mild contrast:

• the male roommate is quiet
• the new female roommate likes listening to music in the evening

So a sounds natural because it suggests:

• while
• whereas
• and on the other hand

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

The neutral order here is very natural:

• Mój współlokator jest cichy, a nowa współlokatorka lubi słuchać muzyki wieczorem.

But some parts could be moved for emphasis. For example:

• Wieczorem nowa współlokatorka lubi słuchać muzyki.
• Nowa współlokatorka lubi wieczorem słuchać muzyki.

These all mean roughly the same thing, but the emphasis changes.

For learners, the safest choice is:

• keep the subject near the beginning
• put the verb fairly early
• leave time expressions like wieczorem toward the end unless you want to emphasize them

In the present tense, Polish often omits the verb to be in some contexts, but not usually when using być as the main verb with an adjective in a standard sentence like this.

So:

• Mój współlokator jest cichy = correct and natural

Without jest:

• Mój współlokator cichy = not correct as a normal full sentence

Polish does omit to be in some other types of expressions, but here jest is needed.

These words can look intimidating, but they are not as bad as they seem once you break them up:

• współ-lokator
• współ-lokatorka

A few useful pronunciation points:

• w sounds like English v
• ł sounds like English w
• ó sounds like u
• cz sounds like English ch in chop
• sz sounds like English sh

So współ sounds roughly like fspuw or vspuw to an English speaker, though the exact sound is Polish.

You do not need perfect pronunciation immediately. The most important thing is to recognize:

• ł = w
• ó = u
• Polish spelling is usually consistent once you learn the letter sounds

It can describe both people and things.

For people, cichy can mean:

• quiet
• not loud
• reserved

For things or places, it can mean:

• quiet
• silent
• peaceful

Examples:

• On jest cichy. = He is quiet.
• To jest ciche miejsce. = This is a quiet place.
• Mam cichy komputer. = I have a quiet computer.

So in your sentence, cichy describes the roommate as a quiet person.

Yes, it normally suggests a general preference or habit.

• lubi = likes
• so the meaning is not necessarily she is listening right now
• it means she likes to listen to music in the evening

If you wanted to describe something happening right now, you would usually use a different structure, for example:

• Nowa współlokatorka słucha muzyki. = The new female roommate is listening to music.

So:

• lubi słuchać muzyki wieczorem = a usual preference / habit
• słucha muzyki = an action in progress or a simple factual action, depending on context