In particular, what commands do I run from the terminal?
Without a home directory
sudo useradd myuser
With home directory
sudo useradd -m myuser
Then set a password
sudo passwd myuser
Then install the shell
sudo usermod -s /bin/bash myuser
Here is the command that I almost always use (adding kevin user):
useradd -d /home/kevin -s /bin/bash -m kevin
Basically 2 teams for this ...
You must run them using root. Just read their manuals to find out how to use them.