Time for action — resizing windows
Notice the black line between the Blender windows:
Move the cursor over one of these lines and you will see a double-headed arrow.
While the double-headed arrow is displayed, hold down the left mouse button (LMB) and move your mouse perpendicular to the line. The windows on both sides of the line will resize.
What just happened?
You selected the line between two windows and moved it to resize the windows. Blender's windows do not overlap. If you make one bigger, the one next to it gets smaller. Unlike many window-based interfaces, you don't end up with a stack of windows that you have to search through to find which window you were working in.