A step up from N5: words for talking about feelings, plans, work, school, and everyday trouble. Still no conjugation tables, just words grouped by where you'll actually need them.
Both the N5 and N4 exams score out of 180 points total, split into two sections: Language Knowledge and Reading (120 points) and Listening (60 points). You need 90 out of 180 overall, but you also have to clear a minimum score in each section separately, so one strong section can't cover for a weak one.
That means every minute you spend memorizing grammar has to actually earn points on test day. Some particles are simple enough that a little study locks in the point almost every time. Others have so many overlapping jobs and native-speaker gray areas that even hours of study won't make you meaningfully faster than a guess. Spend your limited prep time where it pays off, and treat the rest as a quick guess you move past.
If a question hinges on one of these four, take your best guess and move on. Chasing certainty here costs more time than it's worth.