How to use Linux whatis command

Usage: whatis [OPTION...] Keywords...

 -d, --debug output debugging information -v, --verbose output detailed warning messages -r, --regex interpret each keyword as a regular expression -w, --wildcard include wildcards in keywords -l, --long do not truncate output to terminal width -C, --config-file=FILE use this user configuration file -L, --locale=LOCAL define the locale to use for this search -m, --systems=SYSTEM use manual pages from other systems
 -M, --manpath=path Set the search path for manual pages to 'path'
 -s, --sections=LIST, --section=LIST search only these sections (colon-separated)
 -?, --help give this help list
   --usage give a short usage message
 -V, --version print program version

[deng@localhost ~]$ whatis ls
ls (1) - list directory contents ls (1p) - list directory contents

[deng@localhost ~]$ whatis cp
cp (1) - copy files and directoriescp (1p) - copy files

[deng@localhost ~]$ whatis chown
chown (1) - change the file ownership
chown (2) - change ownership of a file
chown (3p) - change owner and group of a file

[deng@localhost ~]$ whatis man
man (1) - formats and displays online man pages man (7) - macros for formatting man pages man (1p) - display system documentation
[deng@localhost ~]$

[root@localhost ~]# makewhatis