Phonetics and the IPA 6, Exercise 1: reading the cells

Pair of letters in one cell: the letter on the right is voiced, the one on
the left is voiceless. (Exception noted by Wikipedia: breathy-voiced [ɦ].)

Lone letter in a cell: it represents a voiced consonant.

Shaded cell: an articulation judged impossible or not distinctive.

Example: in the bilabial stop cell, [p] (left) is voiceless and [b] (right)
is voiced. In the nasal row, a lone [m] is a voiced nasal.