When Debian is up an running, you have 6 cli terminals available (ctrl+alt+f1 .... ctrl+alt+f6), and your gui session at ctrl+alt+f7.
Choose any one of the first six for a cli session, then press the 7th to get back to your gui session.
You also have the option to edit the grub boot menu to boot to runlevels one or three (at the grub menu, press the letter e to edit the boot prompt. then enter init 1 or init 3, then press enter). When you are done in cli mode, enter startx to boot up to gui.
Last edited by bigrigdriver; 03-18-2014 at 02:35 PM.