This is the second 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 bais a sound in Mandarin Chinese, whilebe is not.

By the way, don't let the great number of sounds you see represented in these tables alarm you. The majority of these are seldom used.

Table 2: Chinese initials (left) and finals i through iong (top). 

*The final i should not be confused with -i appearing in Table 1. These two finals are pronounced differently and match with different initials.
NOTE
Table 2 finals, when not preceded by an initial, change the i to y.