L'annonce dans le journal parle d'un emploi au centre-ville.

It is the definite article la shortened before a vowel sound. Annonce is a feminine singular noun, so French uses l'annonce instead of la annonce.

So:

• la
  • consonant sound: la maison
• l'
  • vowel sound: l'annonce

Here, annonce most naturally means an advertisement or listing, especially because it is dans le journal and talks about un emploi.

So in this sentence, L'annonce dans le journal is best understood as the ad in the newspaper or the newspaper ad.

Dans le journal means in the newspaper, which is the normal way to say that something appears inside a publication.

• dans le journal = in the newspaper
• sur le journal would usually mean physically on the newspaper, or sometimes about the newspaper, which is not the intended meaning here

So French uses dans where English also often uses in.

Parler de means to talk about.

The verb parler often takes de when you say what the topic is:

• parler d'un film = to talk about a movie
• parler de politique = to talk about politics

So:

• L'annonce ... parle d'un emploi = The ad talks about / mentions a job

Because parler needs de before the thing being discussed: parler de quelque chose.

So the structure is:

• parle de + un emploi

But de becomes d' before a vowel sound:

• de un emploi is not used
• d'un emploi is correct

So parle d'un emploi literally means talks of/about a job.

Both can relate to work, but they are not always used in exactly the same way.

• emploi usually means a job, position, or employment
• travail often means work in a broader sense, or labor in general

In a newspaper ad, emploi is very natural because it refers to a specific job opening or position.

So here un emploi is better translated as a job than work.

Au is the contraction of à + le.

• à le centre-ville becomes au centre-ville

Centre-ville means downtown or city center, so:

• au centre-ville = downtown / in the city center

This is a very common French contraction:

• à + le = au
• à + les = aux

In the most natural reading, it describes the job.

So the sentence means:

• the ad in the newspaper is about
• a job
• located downtown

French can sometimes allow this kind of attachment to be figured out from context. Here, common sense helps: a job can be downtown, while it would be less likely for the ad itself to be downtown.

Because centre-ville is a fixed compound noun in French. It is written with a hyphen and means downtown or city center.

You should learn it as one unit:

• le centre-ville
• au centre-ville

French has many compound nouns written this way.

It is placed there to show that dans le journal describes the ad.

So:

• L'annonce dans le journal = the ad in the newspaper

If you moved dans le journal later in the sentence, the meaning could become less clear or sound awkward, because it might seem to describe emploi instead.

French word order often helps show which phrase belongs to which noun.

Yes, but it is slightly different.

• L'annonce dans le journal = the ad in the newspaper
• L'annonce du journal = the newspaper's ad / the ad from the newspaper

In many situations, dans le journal is better when you want to emphasize where the ad appears physically or textually.

Not always. Journal can mean several things depending on context, including newspaper, journal, or even news program in some expressions.

But in this sentence, dans le journal most naturally means in the newspaper. The context of an ad and a job makes that meaning the most likely one.