Set newusername as the account name you want the user to have on the server, & newusergithub as that persons github account name. This then takes their public key used with github and allows the user to login to the server via their ssh key.
newusername=bob
newusergithub=bobsgh
sudo useradd -m -d /home/$newusername -s /bin/bash $newusername
cd /home/$newusername/
sudo mkdir .ssh