This package contains the utilities to modify user's passwords, add new users/groups, delete users/groups and more. I'm not going to explain to you what 'password shadowing' means. You can read all about that in the doc/HOWTO file within the unpacked shadow password suite's source tree. There's one thing you should keep in mind, if you decide to use shadow support, that programs that need to verify passwords (examples are xdm, ftp daemons, pop3 daemons, etc) need to be 'shadow-compliant', eg. they need to be able to work with shadow'ed passwords. Shadow'ed passwords are not enabled by default. Simply installing the shadow password suite does not enable shadow'ed passwords. Now is a very good moment to read chapter 5 of the doc/HOWTO file. You can read how you can enable shadow'ed passwords, how to test whether shadowing works and if not, how to disable it again. The documentation mentions something about the creation of npasswd and nshadow after you run pwconv. This is an error in the documentation. Those two files will be be created. After you run pwconv, /etc/passwd will no longer contain the passwords and /etc/shadow will. You don't need to rename the npasswd and nshadow files yourself.