If you're trying to access an interactive process like ftp or a game server, you'll only be able to control it from the terminal that created it. That said, there's a program called screen that you can use to create a virtual terminal that can be opened inside other terminals.
sudo apt-get install screen
To start a screen terminal:
screen -S nameOfScreen
Or if you want to create a screen without connecting to it immediately:
screen -dmS nameOfScreen
And to start a program inside a screen immediately, add the command at the end:
screen -dmS ftpstuff ftp [options for ftp]
You can also reconnect with:
screen -r nameOfScreen
And run a command without entering the screen (useful for scripts):
screen -S gameServer -p 0 -X stuff "alert We're running a backup, expect a bit of lag.$(printf \\r)"
You can disconnect from screen by hitting Ctrl+A followed by Ctrl+D. Try Ctrl+A followed by ? for more help, or read the man page.