How do i back up applications such iphoto etc to my passport essential

You can't just backup individual application setups. You either have to do a full system backup, or backup the files you created. The external disk should have come with backup software to help you do that, or you can use the built-in backup Windows software which is probably a bit harder to use. Your user files that you want to backup should be in the My Documents folder unless you moved them around or the application stores them elsewhere.