Der Flug dauert zwei Stunden.

Because der Flug is the subject of the sentence, so it is in the nominative case.

• der Flug = the flight (nominative)
• den Flug = the flight (accusative)
• dem Flug = to the flight / for the flight (dative, depending on context)

In Der Flug dauert zwei Stunden, the flight is the thing doing the action of lasting, so nominative is required.

dauert is the 3rd person singular form of the verb dauern, which means to last or to take (time).

So:

• Der Flug dauert zwei Stunden. = The flight lasts two hours. = The flight takes two hours.

German often uses dauern where English uses take for time.

Because after dauern, German usually gives the duration directly, without a preposition.

So German says:

• Der Flug dauert zwei Stunden.

Literally, this is closer to:

• The flight lasts two hours.

English can also say for two hours, but with dauern, German normally just uses the time expression by itself.

More examples:

• Das Meeting dauert eine Stunde.
• Der Film dauert drei Stunden.

Because the sentence says zwei Stunden — and after numbers greater than one, you normally use the plural noun.

• eine Stunde = one hour
• zwei Stunden = two hours
• drei Stunden = three hours

So Stunden is simply the plural form of Stunde.

Because German main clauses follow the verb-second (V2) rule.

In this sentence:

• Der Flug = first element
• dauert = second element
• zwei Stunden = the rest

So the structure is:

• Subject + verb + time expression

This is the normal word order for a simple statement in German.

It is a duration expression, and you can think of it as functioning a bit like an accusative of duration.

With verbs like dauern, German often uses a time span directly:

• eine Minute
• zwei Stunden
• den ganzen Tag

You do not need to worry too much about naming the case here at an early stage; the important pattern is:

dauern + length of time

For example:

• Die Reise dauert fünf Tage.
• Der Unterricht dauert neunzig Minuten.

Usually, no — not in standard German for this meaning.

English says the flight takes two hours, but German normally says:

• Der Flug dauert zwei Stunden.

The verb nehmen means to take, but it is not used the same way English uses take for duration in this sentence.

A natural German alternative would be:

• Der Flug dauert zwei Stunden.
• Die Flugzeit beträgt zwei Stunden. = The flight time is / amounts to two hours.

Yes — Flug is masculine, so its basic form is:

• der Flug

In German, noun gender is something you usually need to learn together with the noun itself. So it is best to memorize:

• der Flug = flight
• plural: die Flüge

Learning the article together with the noun will help you build correct sentences more easily.

The plural is die Flüge.

So if you were talking about multiple flights, you would say:

• Die Flüge dauern zwei Stunden.

Notice two changes:

1. der Flug → die Flüge
2. dauert → dauern

That is because the verb must agree with the plural subject.

A common negation would be:

• Der Flug dauert nicht zwei Stunden.
  = The flight doesn’t take two hours.

Here, nicht usually comes before the part being negated — in this case, the duration zwei Stunden.

If you wanted to say the flight is not happening or there is no such flight, you would need a different sentence. But for negating the duration, nicht is the right choice.