Shading Bar

I'm not sure how your screen changed so drastically.  I originally thought you were in "Full Screen" mode but I don't see the "Back to Previous" button at the top of your screen so I would suggest the following:

Hover your mouse over the right side where your window turns into the outliner/properties area.  When you see the double area, Right Click and select "Horizontal Split" or "Vertical Split" if you'd rather.    You will see a white line appear in your screen and your mouse turns into a double arrow with a line through it.  Left click to set this line where you want it.  With the window split, move your mouse over the top left corner of the original screen to the dropdown arrow with the little White Ball Outline showing and choose "3d Viewport". 

You can use the above method to bring back your "Outliner" and "Properties" bars, etc, on the right side, as well.

For the 3D Viewport, put mouse cursor over editor and press shift+F5 or in the header the first icon is the editor selection icon. As for creating a new area for an editor, move mouse cursor to one of the rounded corners it will turn to a target or plus icon. When it does hold left mouse button down and drag into the editor. Left or right depending on corner will split vertically. Up/down will split horizontally. To join areas drag outside of the editor. If you have trouble with that you can go between 2 editors( mouse will turn to double arrows) and right click then select either horizontal or vertical split. If you choose the wrong one then just press tab to switch. Move split line were you want to split and left click. Join can also be done thru this menu too. Another option is to access this thru view->area menu in the header. 

thank you so much <3