Learn Hardcore Norwegian: Det er for mange folk på bussen. - There are too many people on the bus.

It’s the existential construction equivalent to There is / There are in English. Det is a dummy subject (it doesn’t refer to anything), and er is the present tense of å være (to be).

Why do we need det at the beginning? Can’t we just say Er for mange folk på bussen?

In statements, Norwegian normally requires a dummy subject. Without det, the verb has no subject, so Det er is the standard pattern for "there is/are" sentences. You can drop det only when you invert to form a question: Er det for mange folk på bussen?

What does for mange mean here?

For functions as too, and mange means many. Together, for mange means too many.

Could I say for mye folk instead of for mange folk?

Generally no. Mye modifies uncountable (mass) nouns, while mange modifies countable ones. Folk (people) is treated as countable in this context, so for mange folk is correct. For mye folk would sound odd or very colloquial.

Why use folk instead of personer or mennesker?

Folk is the most common everyday word for people. Personer is more formal (individual persons), and mennesker (“human beings”) sounds more general or serious.

Why is it på bussen and not i bussen?

Norwegians use på with most public transport—på bussen, på toget, på trikken. You use i for cars or taxis—i bilen, i drosjen.

Why is bussen in the definite form here?

You’re talking about the bus you’re on, so you use the definite form bussen. If you meant on a bus (any bus), you’d say på en buss.

How would you turn the statement into a question in Norwegian?

Invert the verb and subject:
Er det for mange folk på bussen? (Are there too many people on the bus?)