Mój brat dojeżdża do pracy autobusem codziennie rano.

Because mój has to agree with brat in gender, number, and case.

• brat = a masculine singular noun
• subject of the sentence = nominative case

So the correct form is:

• mój brat = my brother

Compare:

• moja siostra = my sister
• moje dziecko = my child

So mój is the masculine nominative singular form.

Because brat is the subject of the sentence, and subjects are normally in the nominative case in Polish.

In this sentence:

• Mój brat = the person doing the action

So Polish uses the nominative:

• brat = brother
• mój brat = my brother

If brother had a different role in the sentence, its form could change. For example:

• Widzę brata = I see my brother
  Here brat becomes brata because it is the object.

Dojeżdża comes from the verb dojeżdżać, which often means:

• to commute
• to travel regularly to a place
• literally, something like to get to / arrive by traveling, especially as a repeated action

In this sentence, dojeżdża do pracy is best understood as:

• he commutes to work
• he gets to work regularly

This is a very natural verb here because the sentence describes a routine:

• codziennie rano = every morning

Because dojeżdżać is the imperfective verb, and Polish uses the imperfective for:

• habitual actions
• repeated actions
• routines

Since the sentence says codziennie rano (every morning), it describes something repeated, not a one-time completed event.

So:

• dojeżdżać = to commute / to be commuting regularly
• dojechać = to reach/get there once, successfully, as a completed action

Examples:

• Mój brat dojeżdża do pracy autobusem codziennie rano.
  = My brother commutes to work by bus every morning.

• Mój brat dojechał do pracy o ósmej.
  = My brother got to work at eight.
  (one completed trip)

Pracy is in the genitive case because the preposition do requires the genitive.

• do = to / into / toward
• praca = work
• do pracy = to work

This is a very common Polish pattern:

• do domu = to home / home
• do szkoły = to school
• do sklepu = to the shop

So in this sentence:

• dojeżdża do pracy = commutes to work

Because Polish often uses the instrumental case to express the means of transport.

• autobus = bus
• autobusem = by bus

So:

• jadę autobusem = I’m going by bus
• dojeżdża autobusem = he commutes by bus

This is a very common pattern with transport:

• samochodem = by car
• pociągiem = by train
• tramwajem = by tram
• rowerem = by bicycle

Yes. Autobusem is the instrumental singular form of autobus.

The instrumental case is used in several ways in Polish, and one very common use is to express the instrument or means by which something happens. That includes transportation.

So the logic is roughly:

• autobusem = using a bus / by means of a bus

That is why Polish says:

• piszę długopisem = I write with a pen
• jadę pociągiem = I go by train
• dojeżdżam autobusem = I commute by bus

They do, but they add different kinds of information:

• codziennie = every day
• rano = in the morning

Together:

• codziennie rano = every morning

So:

• codziennie tells you how often
• rano tells you when in the day

You can use them separately too:

• Mój brat dojeżdża do pracy codziennie. = My brother commutes to work every day.
• Mój brat dojeżdża do pracy rano. = My brother commutes to work in the morning.

Here rano functions as an adverbial time expression, and for a learner it is easiest to think of it as meaning:

• in the morning

It behaves like a fixed time expression rather than a normal noun form you need to analyze deeply at this stage.

Examples:

• Wstaję rano. = I get up in the morning / early.
• Pracuję rano. = I work in the morning.

So in your sentence:

• codziennie rano = every morning

Yes. Polish word order is more flexible than English word order because grammatical relationships are often shown by case endings, not position alone.

The neutral sentence is:

• Mój brat dojeżdża do pracy autobusem codziennie rano.

But you could also hear:

• Mój brat codziennie rano dojeżdża do pracy autobusem.
• Codziennie rano mój brat dojeżdża do pracy autobusem.
• Autobusem mój brat dojeżdża do pracy codziennie rano.

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

For example:

• Codziennie rano... emphasizes the time
• Autobusem... emphasizes the means of transport

Grammatically, yes — but the meaning changes slightly.

• Mój brat = my brother
• Brat = brother / the brother

Polish often omits possessives when the ownership or relationship is obvious from context, but if you want to clearly say my brother, then mój is the natural choice.

So:

• Mój brat dojeżdża do pracy... = My brother commutes to work...
• Brat dojeżdża do pracy... = Brother / the brother commutes to work...
  This usually needs context.

Polish has no articles. There is no direct equivalent of English a/an or the.

So Polish simply says:

• brat = brother / the brother / a brother
• autobus = bus / the bus / a bus

The exact meaning depends on context.

In this sentence:

• mój brat already makes the noun specific, so no article is needed
• autobusem simply means by bus

Yes, it can look intimidating. The hardest part is the cluster -jeżdż-.

A rough pronunciation guide is:

• do-jeż-dża

Very approximately for an English speaker:

• do like doh
• je like ye
• ż like the s in measure
• dż like the j in jam

So the middle has two similar sounds close together:

• żdż

That is normal in Polish, even though it feels crowded to English speakers.

A rough approximation might be:

• doyezh-jah
  though this is only approximate

Best approach: practice slowly in parts:

1. do
2. jeż
3. dża

Then combine them.

Usually commutes to work is the better translation here.

Why?

Because dojeżdżać often suggests:

• regular travel
• repeated trips
• getting to a destination from somewhere else
• especially daily travel such as work or school commuting

So:

• idzie do pracy = he goes to work / walks to work
• jedzie do pracy = he goes to work / rides/drives to work
• dojeżdża do pracy = he commutes to work

In your sentence, because of autobusem and codziennie rano, commutes to work by bus every morning is especially natural.