man

The man package includes three tools for finding information and/or
documentation about your Linux system: man, apropos, and whatis. The
man system formats and displays on-line manual pages about commands or
functions on your system. Apropos searches the whatis database
(containing short descriptions of system commands) for a string.
Whatis searches its own database for a complete word.

The man package should be installed on your system because it is the
primary way to find documentation on a Linux system.