Windows 10 Maximizes Every Window

Each time I double click an app or program screen (for example: read an email while I have Outlook opened), the clicked on automatically goes to full screen. The icon in the upper right corner indicates the double window (maximized) but clicking on it does not work to make the window smaller so that I may view the original screen and the one I clicked on. This just happened while using the touch screen in a recent airline flight. I'm sure I 'hit' something I shouldn't have but cannot find the setting that will get me back to default (me controlling the windows sizes). More annoying is that I must 'X' out of the clicked on window and go back to the bottom of the screen to re-open my original app/ program.

Thanks, Brink!! I chose Option One when I got to Tablet Mode and it worked perfectly!! Now I know where to go to turn this option on and off if I prefer.