They take no -s. They take no to. They cannot follow one another, and they have no infinitive and no participle, which is why there is no such thing as to must. That part takes four groups and is then finished. The difficulty is that the same nine words do about thirty different jobs between them, and the word on the page tells you almost nothing about which job it is doing: he may leave at six is permission or possibility, and only the situation decides.
So every one of the two hundred entries names the job. Forty groups of five across six parts: the grammar, ability and permission, obligation and advice, the scale of certainty from must be down to can't be, the whole of the past, and the politeness that decides how people answer you.
Two reference pages at the back are worth finding early - the nine modals in a single table with the substitute verb for each, and the nine-rung certainty scale.
Alex Carter writes practical English books for people who use the language at work and in ordinary life rather than in a classroom. The books are built around complete examples - real sentences, real situations - on the principle that one worked example teaches more than a page of rules.