sudo useradd -d /home/nieuweuser -m nieuweuser
sudo passwd nieuweuser
sudo usermod -s /bin/bash nieuweuser
sudo usermod -aG admin nieuweuser
--Don't forget the -a option in usermod when altering a user. Without it you destroy all groups and replace with the new one.
--In newer Ubuntus, do sudo usermod -aG sudo nieuweuser (to give that user sudo rights)