Select a time when you do not need to access your computer- overnight usually works best. If you choose to back up your entire hard drive, the initial backup could take several hours. Visit Mac 101: Time Machine from Apple to learn more. If something goes wrong, it's easy to restore your computer to a previous date and pick up right where you left off. When active, Time Machine automatically creates a backup of your entire hard drive, including your files and applications. Check out Windows Backup and Restore from Microsoft to learn more. You can also use Windows Backup to save a system image, which creates a backup of your entire hard drive, including your files and any applications you have installed. Windows Backup (also known as File History in Windows 8) allows you to create automatic copies of certain files or folders. To simplify the process, most computers can automatically back up certain files or even your entire hard drive.
You never know when you might need to access your files, so you'll want to back them up regularly to make sure you always have a copy of the most recent version. While it's easy to copy files and folders to an external hard drive, it's also easy to forget.