Although a simple google search would have answered your question, I will answer it briefly
Mobile Terminal is a terminal program for access to the terminal of your jailbroken device
SSH is a network protocol for remote shell(terminal) access to computers
If your jailbroken device has SSHD running you can log into the terminal via SSH, a client like Prompt or iSSH(both in iTunes AppStore, Ive used both, Prompt is my fav) on your iDevice, the 'ssh' client on POSIX systems, or PuTTY on win32/64 systems.
If on your iDevice you use 'localhost' as host. Other machines you use your phones local LAN IP.
If your device is not running an SSHD, you must use a terminal program to access your iDevice terminal, something like Mobile Terminal.