There are several ways to switch between active windows. In most cases, switching between windows is the same as switching between applications.
TOGGLE BETWEEN LAST TWO WINDOWS
Press Alt-Tab once. See Win10 Switch apps
TOGGLE BETWEEN ALL OPEN WINDOWS
Hold Alt down while pressing Tab. Each time Tab is pressed, the focus moves to the icon or thumbnail of the next open window in a round robin sequence. Releasing the Alt key maximizes the last window.
To toggle between 3D views of the open windows in the Aero interface of Windows 7, hold the Windows key down while pressing Tab (see Flip 3D
CLICK ANY VISIBLE PART OF THE WINDOW
If you can see any side or corner of another window on the desktop, click it to make it the topmost window.
When you switch windows, other windows may be temporarily out of view. Just hold Alt down and press Tab until the window you want appears and release the Alt key.