Classifiers, and the one Mandarin cannot copy

A number cannot touch a noun. Something goes between them, as in Mandarin.

個 is the general-purpose one, as in Mandarin. The rest overlap heavily with the Mandarin set and diverge in a few useful places: 架 for vehicles and machines where Mandarin uses 辆 or 台, 間 for rooms, shops and buildings, and 隻 far more widely than Mandarin 只 — animals, one of a pair, and also plates, cups and boats.

The ones to learn first

個	the general one, and people
本	books
張	flat things — paper, tables, beds
隻	animals, and one of a pair
杯	cupfuls
件	clothes, and abstract matters
條	long things — roads, fish, trousers
架	vehicles and machines
間	rooms, shops, buildings

個 is the fallback when the right one escapes you, and it is far more tolerated in Cantonese than 个 is in Mandarin. 件 is worth noting for its second use: 一件事, a matter, where nothing physical is being counted.

啲 — the one with no Mandarin equivalent

啲 is the classifier for an unspecified quantity: some, and the plural. It is everywhere, and there is no single Mandarin word that covers it.

A classifier on its own means “the”

This is the construction worth learning early, and Mandarin has no way to do it. Drop the number and the demonstrative, leave the classifier, and the noun becomes definite — a specific one, already known to both of you.

Mandarin would need 那本书 or 这本书 and would still be pointing rather than simply referring. Cantonese does with one syllable what English does with the, and it is one of the clearest signs that the two languages are not the same grammar in different clothes.

Dropping the 一

With a number of one, the 一 is usually left out and the classifier stands alone — which reads as a rather than one, and is distinguished from the definite use above only by context.