In earlier versions of ubuntu, I could install wireless cards using terminal and ndiswrapper. In later versions I don't see an obvious way to get to the terminal mode.
If by "terminal mode" you mean the TTY, it's the same as older versions of Ubuntu: Ctrl+Alt+1. You can replace 1 by any number between 1 and 6. The 7 will bring you back to graphic desktop. TTY is a complete independent session without graphical interface, so you'll need to log in first.
If you just want to open a terminal window, just type Ctrl+Alt+T.