How to quick switch between console and vim

# touch test.txt
# vim test.txt
// Input some words in the VIM editor.
// Ctrl+Z to bring the VIM Editor to backround.
// And now you come to the console again.
# ls
> test.txt
// Now, you finish your work in console.
// "fg" command brings your VIM Editor to the front again.
# fg
// At last, you are in VIM Editor.