Le car de remplacement part de la gare.

Because un car in French is usually a coach or long-distance bus, not a private car. It is a common false friend for English speakers.

• une voiture = a car / automobile
• un bus = a bus
• un car = a coach, especially for longer trips or replacement transport

So in this sentence, le car is a vehicle carrying passengers, not someone’s personal car.

De remplacement means replacement or substitute.

So un car de remplacement is a replacement coach/bus — for example, one used when a train is not running.

French often uses noun + de + noun where English might use one noun directly before another:

• un bus de nuit = a night bus
• une salle de classe = a classroom
• un car de remplacement = a replacement coach

It is not describing the bus with a regular adjective like remplaçant. The fixed expression here is de remplacement.

Because the subject is Le car, which is third-person singular: it.

The verb is partir = to leave / to depart.
Present tense:

• je pars
• tu pars
• il / elle / on part
• nous partons
• vous partez
• ils / elles partent

Since le car = it, French uses part.

Because the verb partir is commonly used with de to mean to leave from a place.

• partir de = to leave from
• arriver à = to arrive at

So:

• Le car part de la gare = the replacement coach leaves from the station

English speakers often want to use from directly in their heads, and in French that idea is expressed with de after partir.

Because gare is a feminine singular noun: la gare.

When de comes before a definite article:

• de + le = du
• de + la = de la
• de + l’ = de l’
• de + les = des

So:

• la gare becomes de la gare

It is not du gare because gare is not masculine.
It is not just de gare because the sentence is referring to the station, not a station in a general sense.

Usually une gare means a station, and very often a train station unless the context says otherwise.

Common expressions include:

• gare SNCF = railway station
• gare routière = bus station / coach station

In this sentence, la gare will usually be understood as the station relevant to the context, often a train station, especially if a replacement coach is being used instead of a train.

It follows a very normal French word order:

Le car de remplacement + part + de la gare

That is:

• subject = Le car de remplacement
• verb = part
• prepositional phrase = de la gare

A useful thing to notice is that de la gare goes with the verb part. It tells you where the departure happens from, not what kind of bus it is.

So the structure is:

The replacement coach + leaves + from the station

A simple learner-friendly pronunciation would be:

luh kar duh ruh-plass-mahn par duh lah gar

A more careful IPA-style version is:

lə kaʁ də ʁə.pla.sə.mɑ̃ paʁ də la ɡaʁ

A few points:

• Le is often a light luh
• French r in car, remplacement, and gare is a throat sound
• The ending -ent is not pronounced in partent, but here the word is part, so you just pronounce the final t? Actually in part, the final t is normally not pronounced: par
• remplacement ends with a nasal sound: -mɑ̃

So in natural speech, part sounds like par, not like English part.

Yes, that is possible in many contexts.

The difference is mainly vocabulary:

• bus often suggests a regular city or local bus
• car often suggests a coach or longer-distance vehicle

In transport announcements, car de remplacement is very common when passengers are being taken instead of a train. But depending on region and situation, bus de remplacement may also be heard.

So the sentence with car is natural, and the choice reflects the type of vehicle being referred to.