Time Machine is the breakthrough automatic backup that’s built right into Mac OS X. It keeps an up-to-date copy of everything on your Mac — digital photos, music, movies, TV shows, and documents. Now, if you ever have the need, you can easily go back in time to recover anything.
You will need a hard drive that is larger then the drive you would like to backup for use with Time Machine.
If your backup hard drive is external, connect it to your Mac.
Launch Time Machine from the Applications folder.
A popup may appear saying that a storage location for Time Machine backups isn't set up. Click the Set Up Time Machine button.
The Time Machine window will open. Click the padlock at the bottom left of the window if its locked.
A popup will appear asking you to login. Enter your administrator username and password then click OK.
Click the Choose Backup Disk... button.
Select the drive you would like to use as your backup drive from the list of available hard disks. Then click the Use for Backup button.
Time Machine will then set itself to begin the initial backup in 120 seconds. Click the Options button.
You will be presented with a Do not backup list. Press the + button.
Select a file or folder you would like to exclude from backup and then click the Exclude button.
You will notice this file or folder gets added to the Do not backup list. Click the Done button when you are finished adding to the list.
Time Machine will then automatically begin its initial backup. This may take some time. For the initial backup, Time Machine copies the entire contents of the computer to your backup drive. It copies every file exactly (without compression), skipping caches and other files that aren’t required to restore your Mac to its original state. Following the initial backup, Time Machine makes only incremental backups — copying just the files that have changed since the previous backup.