$ whatis date date (1) -display or set the date $
The number in parentheses after the command name in the previous example indicates the Reference Manual section to which this command belongs. Commands are grouped into various categories according to function. Most user commands are in section 1. By common convention, the section number is displayed in parentheses after the name of the command. You can find the printed manual reference page for a command in alphabetical order within its group.
The whatis command is only available if your system administrator has set up a special database of command descriptions.