This is the fourth of four tables illustrating which pairings of initials and finals do occur in Mandarin Chinese and, by omission, which do not.
The initial b, for instance, may be paired with a, but not with e, since ba is a sound in Mandarin Chinese, while be is not.
By the way, don't let the great number of sounds you see represented here alarm you. The majority of these are seldom used.
And in Table 4, as you see below, the possible initial + final pairing are few in number. Which is a good thing, because I think it would actually hurt to say züan or shün.