Specifically, what commands do I run from the terminal?
Without a home directory
sudo useradd myuser
With home directory
sudo useradd -m myuser
Then set the password
sudo passwd myuser
Then set the shell
sudo usermod -s /bin/bash myuser
Here's the command I almost always use (adding user kevin):
useradd -d /home/kevin -s /bin/bash -m kevin
There's basicly 2 commands to do this...
You have to run them has root. Just read their manuals to find out how to use them.