Learn Italian: La maggioranza vuole partire subito. - The majority wants to leave immediately.

La maggioranza (the majority) is a collective noun. Even though it describes a large group of people, the grammatical word itself is strictly singular. In Italian, you must always match the verb to the grammar of the noun, not the idea behind it. Therefore, we use the third-person singular verb vuole, never the plural vogliono.

Why isn't there a preposition like a or di between vuole and partire?

Volere (to want) is a modal verb, just like dovere (must) and potere (can). When a modal verb is followed by another action, the second verb stays in the infinitive form (here, partire) and connects directly without needing any prepositions in between.

Could I use uscire instead of partire to say they want to leave?

It depends on the context. Partire implies departing on a journey or leaving for a destination (like catching a train or going on vacation). If the majority simply wants to step out of a room or leave a building, you would use uscire (to go out) or andarsene (to leave / go away).

I sometimes confuse subito with "suddenly". What is the exact difference?