Spotkanie trwa dwie godziny.

It is nominative singular, because it is the subject of the sentence: the thing that lasts.

• spotkanie = meeting
• spotkanie trwa = the meeting lasts / is going on

A useful extra point: spotkanie is a neuter noun. Many Polish nouns ending in -e or forms like -anie are neuter.

Trwa is the 3rd person singular present tense form of trwać.

It matches the subject spotkanie, which is singular:

• spotkanie trwa = the meeting lasts
• spotkania trwają = meetings last

So the ending changes because the subject is singular, not plural.

In this sentence, trwać means to last.

So Spotkanie trwa dwie godziny means that the meeting has a duration of two hours.

But trwać can also mean to continue or to still be going on, depending on context:

• Spotkanie jeszcze trwa. = The meeting is still going on.

So the core idea is continuing in time.

Because godzina is a feminine noun, and the numeral 2 changes for gender.

• dwa is used with many masculine and neuter nouns
• dwie is used with feminine nouns

So:

• dwie godziny = two hours
• dwa spotkania = two meetings

This is one of the first numeral patterns learners need to remember in Polish.

Because the sentence is talking about two hours, so the noun must be plural, not singular.

• jedna godzina = one hour
• dwie godziny = two hours

So godzina would only work with one.

Here it is in the accusative, because Polish often uses the accusative of duration to express how long something lasts.

Examples:

• Spotkanie trwa godzinę. = The meeting lasts an hour.
• Spotkanie trwa dwie godziny. = The meeting lasts two hours.
• Spotkanie trwa pięć godzin. = The meeting lasts five hours.

This also explains a pattern that often confuses learners:

• with 1: godzinę
• with 2, 3, 4: godziny
• with 5+: godzin

So dwie godziny is exactly the form you expect after 2.

Because Polish does not have articles like a and the.

So spotkanie can mean:

• a meeting
• the meeting

You understand which one is meant from context, not from a separate word.

That is why Spotkanie trwa dwie godziny can be translated as either:

• The meeting lasts two hours
• A meeting lasts two hours

depending on the situation.

Yes. Polish word order is more flexible than English word order.

The neutral, straightforward version is:

• Spotkanie trwa dwie godziny.

But other orders are possible for emphasis, for example:

• Dwie godziny trwa spotkanie.
  This puts more focus on two hours.

Even though word order can change, the original sentence sounds the most neutral and natural in many situations.

Not here. With trwać, Polish normally just says:

• Spotkanie trwa dwie godziny.

Using przez is more common with many other verbs:

• Pracowałem przez dwie godziny. = I worked for two hours.

So with trwać, the version without przez is the standard choice.

You change the verb:

• Spotkanie trwało dwie godziny. = The meeting lasted two hours.
• Spotkanie będzie trwało dwie godziny. = The meeting will last two hours.

You may also hear:

• Spotkanie potrwa dwie godziny.

That also means The meeting will last two hours, but it uses a perfective verb and often sounds a bit more like stating the full expected duration as a whole.