Once you have set up your Ubuntu or Debain-based server you won't have any users and will have to login and use the root user this can be a security risk especially for a vps open to the internet.
Creating a user is simple we will use the included adduser command followed by the username of the user in my case I will use invaliduser.
adduser invaliduser
you then will be prompted to enter a password for that user make sure it's secure being at least 14 characters long including upper/lower case letters, numbers, and special characters.
after you have entered your password and verified it you will be prompted to enter other information this information is not required so you can just go ahead and click enter until it asks you if it is correct.
Now you have created your new users you might want to give it root/sudo privileges you do so by using the usermod to add that user to the sudo group replacing invaliduser with your username.
usermod -aG sudo invaliduser
once you have done that you can test your new user by logging in with their details and running a command as sudo.