Een miljoen mensen wachten.

Here een miljoen usually means a million.

Dutch een can be:

• the indefinite article: a / an
• the number one

In this sentence, the basic meaning is simply a million people are waiting. If you want to strongly emphasize the number one, Dutch often writes één with an accent:

• Één miljoen mensen wachten. = One million people are waiting.

So:

• een miljoen = neutral, normal
• één miljoen = stressed or contrastive

The singular is mens.

So:

• mens = person / human
• mensen = people

This is an irregular plural, so you just have to learn it as a form:

• een mens
• twee mensen

Because the subject refers to more than one person, so Dutch uses a plural verb.

Compare:

• De man wacht. = The man waits / is waiting.
• De mensen wachten. = The people wait / are waiting.

With numbers, Dutch also uses the plural:

• Drie mensen wachten.
• Honderd studenten wachten.
• Een miljoen mensen wachten.

So wachten is the correct present-tense plural form here.

This is a very common learner question, because in Dutch the plural present form often looks exactly like the infinitive.

For wachten:

• infinitive: wachten = to wait
• present plural: wachten = wait / are waiting

You can tell from the sentence structure. In a normal main clause, after the subject comes the finite verb:

• Een miljoen mensen wachten.

Here wachten is the verb of the sentence, so it means wait / are waiting, not to wait.

If it were really an infinitive, you would normally need another verb:

• Een miljoen mensen willen wachten. = A million people want to wait.

It can mean either, depending on context.

Dutch simple present often covers both:

• a general fact / habitual action
• an action happening now

So Een miljoen mensen wachten can mean:

• A million people wait
• A million people are waiting

English usually chooses between simple present and present continuous more clearly than Dutch does.

Because this is a normal Dutch main clause with the subject first and the verb second.

The basic pattern is:

• subject + finite verb + rest

So:

• Een miljoen mensen = subject
• wachten = finite verb

Dutch main clauses follow the verb-second rule. That means the finite verb is in the second position. If another element comes first, the verb still stays second:

• Vandaag wachten een miljoen mensen. = Today, a million people are waiting.

So the original sentence has the most straightforward word order.

Yes, but it changes the emphasis.

• Een miljoen mensen wachten. = neutral statement
• Één miljoen mensen wachten. = emphasizes one million

You would use één if you want contrast or stress, for example:

• Niet honderdduizend, maar één miljoen mensen wachten. = Not one hundred thousand, but one million people are waiting.

Without that special emphasis, plain een miljoen is more natural.

Because after a number, Dutch normally uses the noun directly, without another article.

So you say:

• drie boeken
• tien studenten
• een miljoen mensen

Not:

• een miljoen de mensen

This works much like English:

• three books
• ten students
• a million people

The number phrase already determines the noun.

Not always.

Wachten can be used on its own if you just mean to wait:

• De mensen wachten. = The people are waiting.

If you say what they are waiting for, you usually use op:

• De mensen wachten op de bus. = The people are waiting for the bus.
• Een miljoen mensen wachten op hulp. = A million people are waiting for help.

So in your sentence, wachten without op is completely fine because no object is mentioned.

A rough pronunciation guide:

• Een → like uhn with a very weak vowel
• miljoen → roughly mil-YOON
• mensen → roughly MEN-suh(n)
• wachten → roughly WAKH-tuh(n)

A few notes:

• g/ch in Dutch is the famous throat sound; in wachten, the ch is not like English ch in chair
• een is often unstressed and reduced in normal speech
• the stress in miljoen is on the second syllable

So the whole sentence sounds approximately like:

uhn mil-YOON MEN-suh(n) WAKH-tuh(n)

That is only an approximation, but it is a useful starting point.