Create user without password

Creating the user is easy. As root type:

adduser 

and fill in the required information. Provide the user with a password (it is irrelevant which passwrord). Now we will remove the password and enable the account:

passwd -d -u 

The -d switch removes the password, and the -u switch unlockes the account.
The user can now login without entering a password.

Create a new password for the user

This works for any user! Just type:

passwd 

and fill in new password.

Lock the user account

If there is nobody using the account, but you want to save it for later use... just lock the account:

passwd -l 

and ready. You can unlock it again at a later time by typing:

passwd -u 

Remove a user

If there is no more use for the user account, and you want to remove it... just do the following (the following command will remove the users home folder, if you want to keep it... do not enter the -r switch... and/or make a backup of the home folder!):

userdel -r