When you click and drag a window by its tab, the window shrinks and becomes transparent.
Next, I open Documents and it too has a tab on its window. Now, in order to group the Computer window and the Documents window into a single multi-tabbed version of Windows Explorer, I click on the Documents window's tab and drag it towards the tab on the Computer window. As I do, the Documents window shrinks in size and becomes transparent, as shown.
Greg Shultz is a freelance Technical Writer. Previously, he has worked as Documentation Specialist in the software industry, a Technical Support Specialist in educational industry, and a Technical Journalist in the computer publishing industry.