This is an archive of past FreeBSD releases; it's part of the FreeBSD Documentation Archive.
show is to show a letter in your current folder. Like inc, show is a fairly straightforward command. If you just type show and hit return then it displays the current message. You can also give specific message numbers to show:
tempest% show 32 45 56
next is used to move onto the next message and prev will go to the previous message. Both commands have an implied show command so that when you go to the next message it automatically displays it.