Displaying the function of a command (whatis command)

The whatis command looks up a given command, system call, library function, or special file name, as specified by the Command parameter, from a database you create using the catman -w command.

For information about the catman -w command, see catman -w. The whatis command displays the header line from the manual section. You can then issue the man command to obtain additional information. For more information about the man command, see man.

The whatis command is equivalent to using the man -f command.

To find out what the ls command does, type the following:
whatis ls 
The system displays information similar to the following:
ls(1)  -Displays the contents of a directory.