A Linux system has up to 63 virtual consoles (character devices with major number 4 and minor number 1 to 63), usually called /dev/ttyn with 1 n 63. The current console is also addressed by /dev/console or /dev/tty0, the character device with major number 4 and minor number 0. The device files /dev/* are usually created using the script MAKEDEV, or using mknod(1), usually with mode 0622 and owner root.tty.
Before kernel version 1.1.54 the number of virtual consoles was compiled into the kernel (in tty.h: #define NR_CONSOLES 8) and could be changed by editing and recompiling. Since version 1.1.54 virtual consoles are created on the fly, as soon as they are needed.
Common ways to start a process on a console are: (a) tell init(8) (in inittab(5)) to start a getty(8) on the console; (b) ask open(1) to start a process on the console; (c) start X - it will find the first unused console, and display its output there. (There is also the ancient doshell(8)?.)
Alt and !AltGr? refer to the left and right Alt keys, respectively]; (b) use Alt+!RightArrow? or Alt+!LeftArrow? to cycle through the presently allocated consoles; (c) use the program chvt(1). (The key mapping is user settable, see loadkeys(1); the above mentioned key combinations are according to the default settings.)