How to open Fedora without a user password?

You can do it two ways:

1. Open System Settings => Users => Click icon Automatic Login

2. Edit /etc/gdm/custom.conf, add theses lines:

[daemon]
AutomaticLoginEnable=true
AutomaticLogin=mz2

According to the passwd man page:

-d     This is a quick way to delete a password for an account. It will
          set the named account passwordless. Available to root only.

so you can do this (as root):

passwd -d mz2

then you can login without a password

In Gnome, you can follow these steps.

Click ..

1. Activities - Show Applications - Settings - Users.

Here you will see your users details for login.
Make the password - None.
Automatic Login - ON.

Then restart the PC. Problem solved.