Perspectives provide combinations of views and editors that are suited to performing a particular set of tasks. For example, you would normally open the Debug perspective to debug a Java program.
To open a new perspective:
When the perspective opens, the title bar of the window it is in changes to display the name of the perspective. In addition, an icon is added to the shortcut bar, allowing you to quickly switch back to that perspective from other perspectives in the same window.
By default, a perspective will open in the same window. If you would rather it opened in a new window, change the setting in the General > Perspectives preference page.