Left Command key does not have the same function as the Right Command key Since updating my computer to Mavericks all my commands have gone wonky.

My main key problem is my left command key. The right one works correctly with all the shortcuts I use, but the left one zooms out the screen and puts similar applications side by side.

I've tried a lot with System Preferences but since I am new to Mavericks it's hard to find what I am looking for.
Go to System Preferences > Mission Control and check the shortcut for Application windows. It must be set on the left ⌘ key (this must be the only OS X section that accepts single modifier keys).

Mission Control http://cdn.mactrast.com/wp-content/uploads/2013/10/Mission_Control-582x480.png