Using Debian 8 and my settings for users has no option for adding new ones. I used xterm to use the useradd command, but while when repeat it get message that the inputted user already exists, but it doesn't show up anywhere. How can I add these users so can employ them?
Switch user or login all have only the one original user.

please paste here the commands you tried and the output they produced.

As I remember it useradd does not create the necessary directories/files for a new user only the user itself the adduser command should be used for that complete usable user.

Yes. It's there in the manual page(s). There are two utilities that are unfortunately similar in name: useradd and adduser. The former is for scripts, the latter is for interactive work and will prompt you for input. If you are not sure which is which check the manual page before setting out.

Not really true, useradd creates all necessary things, unless you do not want it to create them. But adduser is more user friendly and should be used on Debian and Debian based systems, simply because you can. One of the things useradd does not create is password for new user, you must set it manually with passwd. For short, but very useful intro to useradd command follow this link.

For bit more explanations, as where are config files where you can change some values and how to do it follow this link.

try sudo adduser instead, they both are valid - depeneding on which one is installed.

adduser username ... then passwd (same) username

I had the user names being recognized, but with no passwords or login; so I used:
passwd bil
entered password
re-entered password

was informed all now created, but when I tried to login with: bil [and then the password in provided box] was informed: cannot enter home directory. using /.
then message box: message call to lnusertemp failed (temporary directories full?) (check your installer)

Have no idea what it is talking about, so tried: passwd -S bil
and got: bil L 04/11/2017 -1 -1 -1 -1

Any idea what I've done wrong and how to fix it?

You used the wrong command for creating a workable user. To fix as root mkdir /home/bil then cp /etc/skel/* /home/bil/ next use the vipw command and go down to the line that has the user bil in it and edit the directory used to /home/bil lastly chown -R bil:bil /home/bil. Now logout and back in and hopefully it works if I have not left anything out. Alternatively delete the user and add it again using the proper command if memory serves me correctly again there are two commands for that as well the useless one that does not remove everything and the one that does.

Edit: An example of a correct user in the file the part just before the :/bin/bash is where you need to edit the path to /home/bil.

Thanks Happy Tux, and sorry about delay in reply. Worked great and that vipw command simplified all fixes [made several more users and just edited the forms to match what already had for my main user 'wiliam'; only needed to switch shell to bash from sh and up the priority listing to 1001, 1002, etc.].