Step 1: Once you have purchased your hard drive, plug it into the computer. Go to the Apple Menu in the upper left hand side of the screen, and select “System Preferences…”. From here, click on the “Time Machine” icon under the “System” submenu.
Step 2: Make sure the “Off On” slider is in the “On” position and then push the “Change Disk…” button. Now choose your new hard drive from the list provided. If you only have one external drive plugged in it should be the only one of the list. Now push the “Use for Backup” button. Time machine will now do one long initial backup of your system, and after that is done will do much shorter backups every hour. It will save hourly backups for the last 24 hours, daily backups for the past month, and weekly backups for as long as possible.
Step 3: To restore data from time machine, navigate to your Applications folder and open the Time Machine application.
Step 4: Just navigate to the document you want through the finder window. Once you have found your document, choose the backup point you want to restore it from. This can be done by pushing the forward and back arrows on the lower right hand side of the screen, or by selecting a point in time from the timeline on the right side of the screen. Once you have selected the file and time you wish to restore, push the restore button in the lower right.