"Населення цього міста - два мільйони людей."
Переклад:The city has a population of two million people.
When it is a specific number, million is singular. When it is unspecified, you use the plural.
So there are two million people in the city.
There are millions of people in the city.
It's the same with hundreds, thousands, billions...
Two hundred people.
Hundreds of people.
Seven thousand people.
Thousands of people.