To debug the SharePoint project, we frequently add the dll files to GAC, and copy html, css files to the SharePoint special folders, restart IIS, then refresh the page to start the w3wp.exe, finally attach the VS debugger to the process. The extension is to make it a bit easier.
1. Go to Tools - Options - VS xOP - Attach IIS,
select the web URL which the debugger will be attached to(behind the scene, the debugger is attached to the w3wp based on the application pool instead of the web URL. So if the URLs in the dropdown are not exactly the same as the one you are working on, it's OK).
If you have a Powershell file to add the dll files to GAC, etc, the extension can run it automatically. In the command textbox, enter the path for Powershell(typically it's "C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe"); in the Argument textbox, enter "-File <powershell file>".
If Reset IIS checkbox is checked, "iisreset" command will be run.
2. To use it, first compile the project, then click the button "Attach IIS" under Tools, or use the shortcut Alt + Space.