I had some success today getting two apps to appear on the same screen, or one app to appear along with the desktop.
Here's how I did it: When you click on an app and it takes up the entire screen, put your cursor on the left side of the screen, push the left mouse button, and slowly drag to the right. This will re-size the app and allow the app to run alongside the desktop. My laptop will not consistently do this - I have to play around with it to find the sweet spot. Sometimes the sweet spot is the center of the left edge, sometimes it's at the top left corner, so you may need to play around with yours to find the right place on your screen.
Unfortunately this also screwed up the placement of the desktop icons, but I can live with that.
You can't re-size the apps like you can a window on the desktop. On the desktop you can grab the corner of an open window and drag it up/down/left/right or diagonally to re-size the window. Well, so far with Windows 8.1, I can only drag the window left and right, not up and down or diagonally.
If you drag the window from the top to the bottom it closes the window. If you drag the window from the bottom upwards, nothing happens. Dragging it from left to right is the only way to re-size it. So far I haven't found a way to re-size the height of the window.
While this is an improvement over Windows 8, it still seems like a step backwards from Vista & Windows 7.
Bob