Before you can use Time Machine, you need to select a backup destination. You can back up your files to:
An external hard drive purchased at We Love Macs & connected to a USB, FireWire, or ThunderBolt port on your Mac
Setting up Time Machine is as simple as connecting an external drive to your Mac. If you haven't already specified a backup device, Time Machine asks you when you connect a blank drive to your Mac if you want to use it for backing up.
Click "Use as Backup Disk" to select this drive as your backup destination.
Select the option to Encrypt backups if you want to prevent other users from accessing your backup without a password.
Your Time Machine drive needs to be formatted as Mac OS X Extended (Journaled). If you select an NTFS or FAT-formatted drive, Time Machine prompts you to reformat the drive. Important: Reformatting erases any files on the destination drive. If you're not sure if you want to erase the drive you connected, choose a different drive.
Backing up happens automatically when your Time Machine drive is available.