There are old ways and new ways to switch between open applications in Windows 8, depending on whether you have a keyboard and mouse or must rely on touch only. If you have a keyboard, mouse and touchscreen, you can use all the following methods:
Cycle Through Icons
Cycle Through Apps
Point to upper left corner and click.
From left edge of screen, swipe right.
Via Side Menu
Point to upper left corner of screen and move
mouse down the edge.
From left edge of screen, swipe right
about an inch and back again.
The Old Way - Press Alt-Tab
Holding Alt down and pressing Tab highlights the icons of all open apps in round robin sequence. Letting go of Alt brings the highlighted app on screen. Each app is an icon, whether desktop or tablet style.
A New Way - Side Menu
No matter how many desktop apps are open, this side menu shows the desktop as one icon. See Win8 Sidebar