If the program you want to uninstall contains common files, this common files step will appear.
The common files of the application are .DLL, .OCX and other files which are installed in the WINDOWS folder or in other folders such as WINDOWS\SYSTEM and WINDOWS\SYSTEM32. These files may also be used by applications other than the one you are uninstalling. This is why we recommend you to never uninstall the common files - that is, to uncheck them all before pressing the Next button.
The Select All button selects all the items of the application.
The Select None button unselects all the items of the application.
The Next button uninstalls the application.
See also: The other steps of the uninstall wizard