Learn Croatian: Moraju poštovati pravilo. - They must respect the rule.

In Croatian, pronouns like 'they' (oni) are usually dropped. The verb ending tells you who is doing the action. The -ju ending on moraju clearly means 'they must'.

How do we connect the two verbs moraju and poštovati?

You just put them side by side! The first verb (moraju) changes to match the subject, and the second verb stays in its dictionary form (the infinitive). Here, that is poštovati (to respect), exactly like saying 'must respect' in English.

Why does morati become moraju for the 'they' form?

For many verbs that end in -ati in their dictionary form, the 'they' form is made by replacing the -ti with -ju. So, morati becomes mora- plus -ju, making moraju. Another common example you might know is imati (to have) becoming imaju (they have).

Is the word pravilo (rule) in a special case here?

Yes, it is in the accusative case because it is the direct object receiving the action (it is what is being respected). Luckily, for neuter words ending in -o like pravilo, the accusative case looks exactly identical to the basic dictionary form!