Learn Hardcore Croatian: Kamera prati pokret kamiona. - The camera follows the movement of the truck.

Kamera is the subject of the sentence, so it is in the nominative singular. It is a feminine noun, and its dictionary form is also kamera, so here it appears in its basic form.

What exactly is prati here?

Here prati is the 3rd-person singular present tense of pratiti, meaning follows, tracks, or monitors.

It agrees with the singular subject kamera:

ja pratim = I follow
ti pratiš = you follow
on/ona/ono prati = he/she/it follows

A useful warning: prati can also be the infinitive of a different verb meaning to wash. In this sentence, though, it is clearly the present-tense form of pratiti.

Why is it pokret, not pokreta?

Because pokret is the direct object of prati, it is in the accusative singular.

The noun pokret is masculine inanimate, and for masculine inanimate nouns, the accusative singular looks the same as the nominative singular. So:

nominative: pokret
accusative: pokret

That is why the form does not change here.