Tabs are everywhere within Visual Studio. By default each time a new window is opened a new tab is creates. Many times a lot of tabs can make moving around quickly seem a bit difficult. Within Visual Studio the <CTRL> + <TAB> key open a dialog similar to the Windows Alt-Tab dialog that shows all the open documents.
Using this dialog you can choose files to open by pressing the <CTRL> + <TAB> again. Also, the arrow keys allow the selection of the Active Tool Window.