Le train direct part aujourd’hui.

Le means the.

French usually uses an article before nouns much more consistently than English does. So le train direct is the normal way to say the direct train. Leaving out le here would sound ungrammatical.

In French, many adjectives come after the noun, not before it.

So:

• un train direct = a direct train
• le train direct = the direct train

English speakers often want to put adjectives first, but in French adjective position depends on the adjective. Direct normally comes after the noun here.

Because train is a masculine singular noun.

French adjectives agree with the noun they describe:

• masculine singular: direct
• feminine singular: directe
• masculine/feminine plural: directs / directes

Since le train is masculine singular, the correct form is direct.

Partir is the infinitive, meaning to leave / to depart.
In the sentence, the verb has to be conjugated to match the subject le train.

Because le train is third-person singular, the present tense form is part.

A few forms of partir in the present tense are:

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

So Le train direct part aujourd’hui is grammatically the same kind of structure as The train leaves today.

French often uses the present tense for scheduled or near-future events, just like English can.

Compare:

• The train leaves today.
• Le train direct part aujourd’hui.

This is very natural in French. If you want to stress that the departure is about to happen, French can also use the near future:

• Le train direct va partir aujourd’hui.

But the simple present is completely normal for timetables, plans, and scheduled events.

This is a very common question.

• partir = to leave / to depart
• quitter = to leave something or someone behind

A train departs, so French uses partir:

• Le train part. = The train leaves / departs.

But with quitter, you need a direct object:

• Le train quitte la gare. = The train leaves the station.

So in your sentence, part is the natural choice because the idea is that the train itself is departing.

Yes. Aujourd’hui is fairly flexible.

These are all possible, though they may sound slightly different in emphasis:

• Le train direct part aujourd’hui.
• Aujourd’hui, le train direct part.
• Le train direct aujourd’hui part. — possible in some contexts, but much less natural here

The version with aujourd’hui at the end is very neutral and common.

Because that is simply the standard spelling of the word.

Aujourd’hui is a fixed modern form that comes from older French. For learners, the important thing is: treat it as one word with a required apostrophe.

So always write:

• aujourd’hui

not:

• aujourdhui
• au jour d’hui

The final t in part is normally silent.

So part is pronounced roughly like par in sound.

A very rough guide to the whole sentence is:

luh tran dee-rekt par oh-zhoor-dwee

A few useful pronunciation notes:

• le is often a light luh
• train has a nasal vowel, so it does not sound exactly like English train
• part ends without pronouncing the t
• aujourd’hui ends with a sound like dwee

Here, direct is an adjective describing train.

It tells you what kind of train it is: a direct train.

It is not working like an adverb. If it were an adverb, it would describe how something happens, but that is not what is going on here. In this sentence, direct belongs to the noun phrase le train direct.