Article: Fortunately, Mac owners have a plethora of options available to them for doing this. Choose whichever method suits you the best. Remember that virtual storage and physical storage each have advantages and disadvantages, and remember that anything you don't back up will be gone forever once you reformat your computer's hard drive. Be thorough.  Back up with iCloud if most or all of your content is legally purchased files from the iTunes store. The iCloud service backs up all such content automatically on a daily basis, as well as details like user settings, text messages, phone contacts, and so on. For most users, iCloud is more of a smartphone option than a computer option. Back up to an external hard drive. This is the time-honored method most people use to back up their computer. Run a program such as Apple's own Time Machine utility, and point it to the external drive you have connected to your computer. The program will create a backup copy of everything except system files. You can also back your drive up manually by literally dragging everything you want to save onto your external hard drive's desktop icon en masse, but this is messy, slow, and less reliable than letting a program take care of it for you, in most cases.  Back up to physical media. When all else fails, if your computer has a writable optical drive (such as a DVD/RW drive), you can purchase a stack of blank discs and manually back up content to the discs, one disc at a time. This isn't recommended, as it's easy to misplace or damage the discs, but in a dire emergency it can help you save data and applications that might otherwise have been lost. Load your Mac's Install disc into the optical drive and reset the computer. As the computer boots up again, hold down the “c” key to force it to boot up from the Install disc. You'll see a list of language options, and then a menu screen. From this point until you've completely finished reinstalling your system software and reset the computer, do not remove the Install disc from the drive for any reason. Select “Utilities” from the menu, and “Disk Utility” from there. In Disk Utility, choose the hard disk you want to erase from the drop down menu and click the “Erase” tab, then click and confirm the “Erase” button. Disk Utility will erase that entire drive.  Erasing a hard drive takes time. Be prepared to wait a while and, as before, don't jostle or move the computer while it's erasing. Be very careful not to select your backup drive by accident. If you're worried you might, just unhook it from your computer before you restart it. Once you're done erasing your hard disk, quit Disk Application to find a Mac Installer window. Click the “Continue” button to view the license agreement. Read it if you want, then accept it and click the hard drive you just erased on the next screen. Click “Install” to install the system software. Once you've finished installing the system software, click “Restart” to restart your Mac and boot up as normal. Your Mac will guide you through initial setup; once you've finished, it's time to update to the latest version of the OS you were using. Visit your account at Apple.com and download and install all the updates you previously purchased. Depending on the method you chose, either load your optical discs sequentially, drag files from your external hard drive, or run Time Machine (or another backup utility) and choose to restore your old files from an external hard drive. All three methods take time, so be patient. If you have data backed up on iCloud, you can simply log in and copy it back to your hard disk.
What is a summary of what this article is about?
Back up files. Restart from disc. Run Disk Utility. Reinstall the system software. Restart and update. Restore your files.