You may have minimized your window or a window may have been put on a different workspace. You can locate your window from the
By switching to the
You can also right-click on the application in the docky. All open windows of an application will be listed. You can click on the window you wish to switch to in the list.
Press
Press
If an application has multiple open windows, there is an arrow below the application icon which is seen when tabbing through the apps. Pressing the down arrow on your keyboard will allow you to tab through the multiple windows.