Jazda samochodem do domu była długa.

Because jazda is a noun, not a verb. It means something like driving, a ride, or a journey by vehicle, depending on context.

So this sentence is built like:

• Jazda samochodem do domu = the drive / driving home by car
• była długa = was long

Polish often uses noun phrases like this, just as English can say The drive home was long instead of Driving home took a long time.

Here jazda means the drive / the trip / the ride.

It does not mean only the physical act of operating a car. In Polish, jazda can refer more generally to traveling in or on a vehicle.

In this sentence, the most natural English idea is:

• The drive home by car was long or
• The car journey home was long

Because samochodem is the instrumental case of samochód.

After nouns like jazda, Polish often uses the instrumental to express the means of transport:

• jazda samochodem = driving / going by car
• jazda pociągiem = traveling by train
• jazda autobusem = going by bus

So samochodem answers the question by what means? or using what vehicle?

Because do means to or toward, and it requires the genitive case.

• dictionary form: dom
• genitive singular: domu

So:

• do domu = to home / homeward
• more naturally in English: home

This is a very common pattern:

• do szkoły = to school
• do pracy = to work
• do miasta = to the city

Because the subject is jazda, and jazda is a feminine singular noun.

In the past tense, Polish verbs agree with the subject in gender and number:

• był = masculine singular
• była = feminine singular
• było = neuter singular
• byli / były = plural

Since jazda is feminine, you need:

• Jazda ... była długa.

For the same reason: adjectives must agree with the noun they describe.

The noun jazda is:

• feminine
• singular

So the adjective must also be feminine singular:

• masculine: długi
• feminine: długa
• neuter: długie

That is why you get:

• Jazda była długa. = The drive was long.

Yes, it is grammatical and understandable, but depending on context, some speakers might prefer more natural alternatives.

Possible alternatives:

• Podróż samochodem do domu była długa. = The journey home by car was long.
• Droga do domu była długa. = The way home was long / The trip home was long.
• Jazda do domu była długa. = The drive home was long.

Your original sentence is correct, but jazda samochodem do domu can sound a little more explicit than everyday speech sometimes needs.

Yes. If it is already clear that the person was traveling by car, you can leave out samochodem.

• Jazda do domu była długa. = The drive home was long.

Adding samochodem makes the means of transport explicit:

• Jazda samochodem do domu była długa. = The drive home by car was long.

So both are possible; it depends on how much information you want to include.

Yes, and in many contexts podróż may sound more neutral or more natural.

Compare:

• Jazda samochodem do domu była długa.
• Podróż samochodem do domu była długa.

Podróż means journey/trip, while jazda is more specifically driving/riding/travel by vehicle.

If you want to emphasize the journey itself, podróż is often a good choice.
If you want to emphasize the drive or travel by vehicle, jazda works well.

Because Polish has no articles like English a/an/the.

So:

• jazda can mean a drive or the drive
• domu can mean home / the home depending on context

The exact meaning comes from context, not from an article.

That is normal in Polish and one of the big differences from English.

The basic structure is:

• Jazda samochodem do domu = subject noun phrase
• była = verb
• długa = predicate adjective

So the sentence literally follows:

• The drive by car home was long

This word order is normal, but Polish word order is flexible. You could change it for emphasis, for example:

• Długa była jazda samochodem do domu.
• Jazda do domu samochodem była długa.

These are still understandable, but the original order is the clearest and most neutral for a learner.

Here it most naturally means long in duration.

So jazda była długa usually means:

• the drive took a long time

Depending on context, długi words can sometimes describe physical length, but with things like jazda, podróż, spotkanie, or rozmowa, the usual meaning is lasting a long time.

Yes. Jazda is a broad word and can have several related meanings, such as:

• riding / driving
• a ride / trip
• in some contexts, motion, racing, or even an idiomatic exclamation in colloquial speech

But in your sentence, because of samochodem do domu, the meaning is clearly the drive home by car. The surrounding words remove ambiguity.