Il volo ritarda a causa della nebbia.

Il is the masculine singular definite article, meaning the.

So:

• il volo = the flight
• volo by itself = flight or I fly in other contexts

In Italian, singular countable nouns usually take an article when you mean a specific thing, so il volo is the normal form here.

Ritarda is the third-person singular present indicative of ritardare.

The subject is il volo, which is third-person singular, so:

• io ritardo = I am late / I delay
• tu ritardi = you are late / you delay
• lui/lei ritarda = he/she is late / delays
• il volo ritarda = the flight is late / the flight is delayed

In English, we often say is delayed or is running late, but Italian can simply use the verb ritardare.

Yes, literally ritarda comes from ritardare, which can mean to delay or to be late depending on context.

With things like trains, flights, buses, Italian often uses the active-looking verb where English prefers a passive or adjective-like expression:

• Il treno ritarda = the train is late / the train is delayed
• Il volo ritarda = the flight is late / the flight is delayed

So the Italian structure is normal, even if English expresses the idea differently.

It is grammatical and understandable, but in many real travel situations Italians more often say:

• Il volo è in ritardo. = The flight is late.
• Il volo è in ritardo a causa della nebbia. = The flight is delayed because of the fog.

So ritarda is fine, but è in ritardo is often the more common everyday phrasing for transport delays.

Yes.

In this sentence it is being used intransitively:

• Il volo ritarda. = The flight is delayed / running late.

But it can also be transitive:

• La nebbia ritarda il volo. = The fog delays the flight.

So the same verb can work both ways, depending on whether you state a direct object.

A causa di means because of, due to, or as a result of.

It is a fixed expression used to introduce the cause of something:

• a causa della nebbia = because of the fog
• a causa del traffico = because of traffic
• a causa del maltempo = because of bad weather

It often sounds a little more formal than simple per, and it is especially common when the cause is something negative or problematic.

Because di combines with the definite article la.

This is a normal Italian contraction:

• di + la = della

Since nebbia is a feminine singular noun, its article is la:

• la nebbia = the fog

So:

• a causa di la nebbia → not used
• a causa della nebbia → correct

This kind of contraction is very common in Italian.

That is a very common difference between English and Italian.

Italian often uses the definite article where English does not. So although English says:

• because of fog

Italian normally says:

• a causa della nebbia

Literally that looks like because of the fog, but it is the standard way to express the idea in Italian.

Sometimes yes, but the meaning and tone are slightly different.

• a causa della nebbia = because of the fog / due to the fog
  This is more explicit and often more formal.
• per la nebbia = because of the fog
  This can sound shorter and less formal, but it is not always the best replacement in every context.

In announcements or formal explanations, a causa della nebbia is very natural.

Yes. Italian word order is more flexible than English.

The sentence given has a neutral order:

• Il volo ritarda a causa della nebbia.

But you could also say:

• A causa della nebbia, il volo ritarda.

That puts more emphasis on the cause first: because of the fog.

Both are correct; the first one is just the more straightforward, neutral version.

Nebbia is a feminine singular noun meaning fog.

So:

• la nebbia = the fog
• della nebbia = of the fog

In this sentence it appears inside the expression a causa della nebbia, where it names the reason for the delay.

Yes. In Italian, the simple present often covers situations that English might express with:

• is delayed
• is running late
• is being delayed

So ritarda can describe a current situation without needing any extra verb. Italian uses the present tense more broadly than English in cases like this.