The corners on your screen are hot corners and give you access to different Windows features.
Bottom Left-hand corner
Toggles between the Start Screen and Desktop (depending on where you are).
Tip: Right-clicking in the left hand corner will open the power user menu.
Top-left corner of the screen
Moving the mouse to the top-left corner and then down will display all the apps running on the computer. Clicking and dragging any of these apps to the left or right-hand side of the screen will snap that app to that side of the screen. Each of these open app icons can also be right-clicked to close or snap.
Right-hand side of the screen
On the full right-hand side of the screen will be given access to the Windows Charms.