Na co dzień korzystam z autobusu, ale latem częściej jeżdżę rowerem.

Na co dzień means on a daily basis, in everyday life, or simply usually / day to day.

It is a fixed expression, so it is best learned as a whole phrase.
In this sentence, Na co dzień korzystam z autobusu means something like:

• I normally use the bus
• In everyday life, I use the bus
• Day to day, I take the bus

Because the verb korzystać requires the preposition z, and z takes the genitive case.

So:

• korzystać z czegoś = to use something
• korzystam z autobusu = I use the bus

This is just how the verb works in Polish. It is worth learning it as a pattern:

• korzystać z telefonu = to use a phone
• korzystać z komputera = to use a computer
• korzystać z pomocy = to use help / benefit from help

Because after z, the noun goes into the genitive case.

The basic form is:

• autobus = bus

But after z with korzystać z, it becomes:

• z autobusu

So:

• korzystam z autobusu = I use the bus

This does not mean from the bus here. Even though z often means from or with, in this pattern it is simply part of the verb korzystać z.

This is a very common question.

Polish makes an important distinction:

• jechać / jadę = to be going right now, in one specific trip, by vehicle
• jeździć / jeżdżę = to go regularly, habitually, or repeatedly, by vehicle

In this sentence, the speaker is talking about a habit:

• latem częściej jeżdżę rowerem = in summer I go by bike more often

So jeżdżę is correct because it describes repeated action, not one journey happening at this moment.

Rowerem is the instrumental case of rower, and it is often used to express the means of transport.

So:

• rower = bicycle
• rowerem = by bicycle

That is why:

• jeżdżę rowerem = I go by bike / I ride a bike

You may also hear:

• jeżdżę na rowerze = I ride a bike

Both are correct, but they feel slightly different:

• jeżdżę rowerem emphasizes the bicycle as the means of transport
• jeżdżę na rowerze is also very common and more literally means I ride on a bicycle

Latem is a very common Polish adverbial form meaning in summer.

So:

• latem = in summer
• zimą = in winter
• wiosną = in spring
• jesienią = in autumn

These are extremely common and natural.

You may also hear w lecie, which can also mean in the summer, but latem is shorter and very common in everyday speech.

W lato is generally not the normal form here.

Częściej means more often.

It is the comparative form of:

• często = often
• częściej = more often

So in the sentence:

• latem częściej jeżdżę rowerem = in summer I go by bike more often

Other useful examples:

• Rzadziej = less often
• Szybciej = faster
• Wolniej = more slowly

Because in Polish, the verb ending usually already shows the subject.

Here:

• korzystam = I use
• jeżdżę = I go / I ride

So the subject ja is not necessary.

Polish often omits subject pronouns unless you want emphasis or contrast.

For example:

• Korzystam z autobusu. = I use the bus.
• Ja korzystam z autobusu, a on z tramwaju. = I use the bus, and he uses the tram.

In the second sentence, ja is added for emphasis or contrast.

Ale means but.

It connects two contrasting ideas:

• Na co dzień korzystam z autobusu = I usually use the bus
• ale latem częściej jeżdżę rowerem = but in summer I go by bike more often

The contrast is between the speaker’s usual habit and what happens in summer.

Not completely. Polish word order is more flexible than English, although some versions sound more natural than others depending on emphasis.

The given sentence is very natural:

• Na co dzień korzystam z autobusu, ale latem częściej jeżdżę rowerem.

You could also say:

• Korzystam z autobusu na co dzień, ale latem częściej jeżdżę rowerem.

That is also understandable, but the original version sounds smoother and more natural in many contexts.

In Polish, changing word order often changes emphasis, not the core meaning.

Both can be translated as something like I use / take the bus, but they are not exactly the same.

• korzystam z autobusu = I use the bus
  This focuses on using the bus as a service or means of transport.
• jeżdżę autobusem = I go by bus / I travel by bus
  This focuses more directly on the activity of travelling by bus.

In many everyday situations, they are very close in meaning.
In this sentence, korzystam z autobusu sounds slightly broader and pairs nicely with jeżdżę rowerem in the second half.