I want to add user with password but when I looked up man useradd it says: -p passwd (use CRYPT(3)). What does it mean? and for example, if I want to add user user1 with password 12345 what should I type?

ps. I tried useradd -p 12345 user1 but it didn't work.

What it means is that you have to pass an encrypted password string
as the argument to your "useradd -p" command. The crypt(3) reference
is telling you where in the man pages (section 3) you can find information
about crypt.

I use the following perl script to encrypt a password when I need to do this:
~~~~~~~~~
#! /usr/bin/perl
($password, $salt) = @ARGV;
$password or die "usage: mycrypt password [salt]\n";
$salt = "cc" unless $salt;
$cryptpw = crypt($password,$salt);
print "$password -> $cryptpw \n";
~~~~~~~~~

In the above script, salt is a two character string that is used as the basis
for the encryption of the password. To use the script, (after saving it as
"myscript" and making it executable) invoke:
./myscript password

Use the string that is generated by the script as the argument after the
-p option in your useradd invocation.

Good luck.

forget adding a password at the time of creation. Do it immediately after. If you have created "user1", then use "passwd user1" and enter the password. Done. No fighting with switches and encryption that is handled automatically by passwd.