Learn Hardcore Croatian: Najava projekcije traje kratko.

najava = the subject of the sentence. It is a feminine singular noun in the nominative case.
projekcije = a noun in the genitive singular, dependent on najava.
traje = the verb, 3rd person singular present tense of trajati = to last
kratko = an adverb, describing how long something lasts, here in the sense of briefly / for a short time

So the basic structure is:

[subject] + [related noun in genitive] + [verb] + [adverb]

Why is projekcije in the genitive case?

Because najava often takes a noun in the genitive to show what is being announced.

So:

This is very common in Croatian. English often uses of, but Croatian often expresses that relationship with the genitive case instead.

So projekcije is not the subject. It is part of the noun phrase najava projekcije.

Is najava projekcije one unit?