How to use the command openssl rand in ubuntu 18.04

lwk@qwfys:~$ man rand |tee /dev/null
RAND(1SSL)                                                                                                       OpenSSL                                                                                                      RAND(1SSL)

NAME
       openssl-rand, rand - generate pseudo-random bytes

SYNOPSIS
       openssl rand [-help] [-out file] [-rand file...]  [-writerand file] [-base64] [-hex] num

DESCRIPTION
       The rand command outputs num pseudo-random bytes after seeding the random number generator once.  As in other openssl command line tools, PRNG seeding uses the file $HOME/.rnd or .rnd in addition to the files given in the
       -rand option.  A new $HOME/.rnd or .rnd file will be written back if enough seeding was obtained from these sources.

OPTIONS
       -help
           Print out a usage message.

       -out file
           Write to file instead of standard output.

       -rand file...
           A file or files containing random data used to seed the random number generator.  Multiple files can be specified separated by an OS-dependent character.  The separator is ; for MS-Windows, , for OpenVMS, and : for all
           others.

       [-writerand file]
           Writes random data to the specified file upon exit.  This can be used with a subsequent -rand flag.

       -base64
           Perform base64 encoding on the output.

       -hex
           Show the output as a hex string.

SEE ALSO
       RAND_bytes(3)

COPYRIGHT
       Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (the "License").  You may not use this file except in compliance with the License.  You can obtain a copy in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>.

1.1.1                                                                                                          2020-05-27                                                                                                     RAND(1SSL)
lwk@qwfys:~$