I've had a Mac for a while but I still don't understand what this feature is.. Sometimes I may have multiple windows open and one of them accidently shifts off the screen onto the left or right, and gets a whole new screen of its own. This is accompanied by 8 small little squares on the bottom center of my computer in two rows of four (with 2 filled indicating I have 2 screens now). Then it takes me forever to figure how to get back to everything being on one screen and I just end up closing all my programs and reopening them in one screen again. So why or how does this happen? How do I prevent this from occurring? And if it does happen, how do I access each screen and use it for its proper reason of actually being there in the first place? Thanks!!