Utilities normally return zero for successful completion and values greater than zero when unsuccessful. Some utilities return different nonzero numbers according to the reason they failed. Beware of testing for a specific nonzero number to indicate failure. (In most cases utilities that may return different nonzero numbers are explicitly documented as doing so. However, you should not rely on this.)
For some utilities, the exit status may reflect only the success or failure of the last action taken (of many). In these cases, this behavior is explicitly documented in the "Exit status" section.
In the ksh, you can use $? to get the exit status of the last command. For more information, see "Parameters" in the documentation for ksh.