Windows 10 introduced a new feature called Task View. It makes it easy to quickly find and switch to an open window. The Task View button is to the right of the Start button.
Click on the Task View button and all open windows on all monitors are displayed as thumbnails.
Click on a window to activate it or move your mouse pointer over a window to display the Close button at the top right of the window.
And the keyboard shortcut for the Task View? Windows+Tab