In Windows 7, as with previous versions, any active programs appear as icons (or tabs) on the Taskbar. What is new in Windows 7, is that you can reorder the icons on the Taskbar to suit your needs. To move an icon, simply drag and drop.
In addition, once you have reordered the Taskbar icons, you can start a new instance of any of the first five programs by pressing Win+1, Win+2, Win+3, etc. For example, if Windows Explorer is the second icon on the Taskbar, you can open a second instance by pressing Win + 2.