Cloning a window in the IDE creates an identical instance of the current window, which you can then navigate in normally. This is useful if you are part way through working with a particular program element, but need to do something in the same browser and then return to your current location.
For example, if you are browsing a package, MyPackage, editing a class called MyClass1, and you decide you need to quickly work with MyPackage.MyClass2, and then return to MyClass1. Rather than lose your place (and perhaps temporarily introduce errors) by exiting MyClass1, clone the package browser. Then browse to MyClass2, make the needed changes, and close the clone. The original browser will still be opened to MyClass1.
To clone a window, select Clone from its Window menu. You can clone the Workbench, program element browsers, inspectors, and the Repository Explorer.