If you install OpenSSH, you need to change your device's root password to prevent the possibility of unsavory people remotely logging into your device using the default password.
Option A: Open Terminal on your desktop and log in over wifi
Follow OpenSSH Guide
Or Option B: Open a SSH client app
To configure your client app on your device: add "127.0.0.1" (which means localhost) as the host/server, "root" as the login username, and "alpine" as the initial password.
Or Option C: Open MobileTerminal
1: Obtain Administrator Access
Note: this first step is only necessary if you are using MobileTerminal. If you logged in via SSH as root, you do not need to do this step, so skip to Step 2.
Run "su root" and provide the root password. The default password as provided by Apple is "alpine".
Here I also run "cd" only to shorten the otherwise very long prompt.
2: Change the root Password
Run "passwd" and type in your new password twice. Please note that your keypresses will not be displayed on the terminal screen (for security).
3: Change the mobile Password
This is the regular user account on the device. Run "passwd mobile" and repeat as directed above.
4: Close your terminal
Congratulations! Your job is done!