Gdy pada deszcz, biorę taksówkę, a taksówkarz pomaga mi z walizką.

Here gdy means when.

In this sentence, gdy pada deszcz = when it rains.

For many everyday situations, gdy and kiedy can both mean when:

• Gdy pada deszcz...
• Kiedy pada deszcz...

Both are natural.
A rough difference is that gdy can sound a little more written or formal in some contexts, while kiedy is very common in speech. In a simple sentence like this, either one works.

Polish does not need a dummy subject like English it.

English says:

• It is raining
• It rains

But Polish simply says:

• Pada deszcz = literally something like falls rain

The verb padać is commonly used for weather phenomena:

• Pada deszcz = it’s raining / it rains
• Pada śnieg = it’s snowing / snow is falling

So there is no separate word for English it here.

The verb brać normally means to take, so biorę taksówkę literally means I take a taxi.

That matches a very common English expression:

• I take a taxi

You could also express the idea differently in Polish, for example:

• jadę taksówką = I go / travel by taxi

The difference is:

• biorę taksówkę focuses on the choice of transportation: I take a taxi
• jadę taksówką focuses on the means of travel: I’m going by taxi

In your sentence, biorę taksówkę is completely natural.

Because taksówkę is in the accusative case.

The noun taksówka is the direct object of biorę:

• biorę co? = what do I take?
• taksówkę

Singular feminine nouns ending in -a often change to -ę in the accusative:

• taksówka → taksówkę
• walizka → walizkę
• kawa → kawę

So:

• taksówka = a taxi
• biorę taksówkę = I take a taxi

Because the verb pomagać takes the dative case, not the accusative.

So:

• pomagać komu? czemu? = to help whom? to what?
• mi is the dative form of ja (I / me)

Compare:

• pomaga mi = helps me
• daje mi = gives me
• mówi mi = tells me

The form mnie is used in other contexts, but after pomagać, you normally use the dative:

• pomaga mi
• pomaga tobie / ci
• pomaga mu
• pomaga nam

Both can mean me, but they are used differently.

In this sentence:

• pomaga mi is the normal, unstressed form.

Mi is usually the shorter, clitic-like form used in ordinary sentences:

• Daje mi książkę.
• Pomaga mi codziennie.

Mnie is often used:

1. for emphasis
2. after some prepositions
3. when the sentence structure requires the full form

Examples:

• On pomaga mnie, nie tobie — better: On pomaga mnie? Actually with pomagać you still want dative, so the emphatic form is mnie only in some dative contexts?
  To keep it simple for learners: after pomagać, the normal everyday form is mi, and if you want emphasis you are more likely to hear:
• On pomaga właśnie mnie.

A very useful practical rule:

• Use mi in ordinary sentences like this one.
• Learn mnie separately in full pronoun patterns and after prepositions like do mnie, dla mnie, beze mnie.

Walizką is the instrumental singular form of walizka.

After z meaning with, Polish often uses the instrumental:

• z walizką = with a suitcase
• z torbą = with a bag
• z dzieckiem = with a child

So:

• walizka = suitcase
• z walizką = with the suitcase / with a suitcase

In this sentence, pomaga mi z walizką means helps me with my suitcase.

Because feminine nouns ending in -a often change to -ą in the instrumental singular.

Examples:

• walizka → walizką
• kawa → kawą
• taksówka → taksówką

So:

• z walizką = with a suitcase
• z taksówką = with a taxi

This -ą ending is very common and worth memorizing early.

Yes. It means:

• helps me with the suitcase
• more naturally in context: helps me with my suitcase / luggage

It suggests the taxi driver helps carry, lift, load, or handle the suitcase.

In Polish, z walizką here works a bit like English with the suitcase:

• Taksówkarz pomaga mi z walizką.
• The taxi driver helps me with my suitcase.

Because Polish, like English, often uses the present tense for general truths, habits, and repeated situations.

So this sentence means something like:

• When it rains, I take a taxi, and the taxi driver helps me with my suitcase.

It is not necessarily happening right now. It can describe a routine or a typical situation.

This is very normal in Polish:

• Gdy jestem zmęczony, piję kawę. = When I’m tired, I drink coffee.
• Kiedy pada śnieg, zostajemy w domu. = When it snows, we stay at home.

Because Polish punctuation usually separates clauses more clearly than English.

Your sentence has two main parts:

1. Gdy pada deszcz, biorę taksówkę
2. a taksówkarz pomaga mi z walizką

The comma after deszcz marks the end of the subordinate clause:

• Gdy pada deszcz, ... = When it rains, ...

The comma before a is also standard in Polish:

• ..., a ...

Here a means something like and, sometimes with a slight sense of contrast or moving to another related action:

• I take a taxi, and the taxi driver helps me...

So the commas are normal and expected.

Here a means and, but it is not always exactly the same as i.

Very roughly:

• i = simple and
• a = and / while / whereas, often linking a new but related piece of information

In your sentence:

• biorę taksówkę, a taksówkarz pomaga mi z walizką

This sounds natural because the second clause adds another related event:

• I take a taxi, and the taxi driver helps me with my suitcase.

If you used i, it might also be understandable, but a is very natural here.

Yes, Polish word order is more flexible than English, though the original version is very natural.

Original:

• Gdy pada deszcz, biorę taksówkę, a taksówkarz pomaga mi z walizką.

Possible variations:

• Biorę taksówkę, gdy pada deszcz, a taksówkarz pomaga mi z walizką.
• Gdy pada deszcz, taksówkę biorę, a taksówkarz pomaga mi z walizką.
  This is possible, but more marked and less neutral.

The usual advice for learners:

• Stick with the original neutral order unless you have a reason to emphasize something.

A few helpful pronunciation notes:

• biorę: the ę at the end is a nasal vowel, though in normal speech at the end of a word it is often pronounced less strongly nasal than learners expect.
• walizką: the ą is also nasal, and before k it is often pronounced something like on/om depending on the phonetic environment, so learners may hear something close to valiskom.

Also:

• rz in taksówkarz sounds like ż
• sz in deszcz sounds like English sh, though deszcz is a consonant-heavy word and can be tricky at first

You do not need perfect nasal pronunciation immediately; being understood matters more.

Yes. Taksówkarz is a standard and very common word for taxi driver.

Related words:

• taksówka = taxi
• taksówkarz = taxi driver

The ending -arz often forms a noun for a person associated with something, though you should learn each word individually rather than assuming every noun works this way.

Yes, you could.

• pomaga mi z walizką = helps me with the suitcase / with my suitcase
• pomaga mi z moją walizką = helps me with my suitcase

Polish often leaves out possessives like my when the meaning is obvious from context. Since it is naturally your suitcase, z walizką is enough.

Adding moją makes it more explicit, but it is not necessary.