Time Machine Preferences on Your MacBook
The Time Machine Preferences pane controls the automatic backups performed by Lion’s Time Machine feature on your MacBook. To enable Time Machine, click the On toggle switch and then select a disk that will hold your Time Machine backup data on the sheet that appears; click Use for Backup to confirm your choice. If you have an external Time Capsule wireless unit, click Set Up Time Capsule.
By default, Time Machine backs up all the hard drives on your system; however, you may not need to back up some hard drives or folders on your MacBook. To save time and hard drive space, Time Machine allows you to exclude specific drives and folders from the backup process.
Click Options and then click the Add button (with the plus sign) to select the drives or folders you want to exclude, and they’ll appear in the Do Not Back Up list.
To remove an exclusion, select it in the list and click the Delete button (with the minus sign). Note the Estimated Size of Full Backup figure increases, and Time Machine adds the item you deleted from the list to the next backup.
By default, Lion warns you when deleting older backup files, but you can turn this off from the Options sheet as well.
You can elect to back up your MacBook immediately by clicking the Time Machine icon in the Finder menu bar and choosing Back Up Now.