Welcome to Backup Club. The first rule is: You must back up!

Sooner or later, you will lose files and/or your hard drove will die, so you have to be prepared. Fortunately, Time Machine--the backup application built in to Leopard--makes backups a no-brainer. With this guide, backing up is even easier.

The first thing you’ll need is an external USB or FireWire hard drive. When in doubt, buy the largest drive you can afford--a 300GB or 500GB drive is a safe bet. Try the Lacie Ethernet Disk Mini Home Edition, Western Digital's WD Passport, or the Western Digital My Book Studio Edition.

1. Turn on Time Machine.
The first time you connect the external hard drive to your Mac, Time Machine will ask if you’d like to use it for backups.

Click Use as Backup Disk and System Preferences will open to display Time Machine preferences.

From now on, Time Machine will do the rest; your first backup will begin automatically in a few minutes.

2. Exclude some items to conserve disk space.
What if you don't want to back up everything on your computer? For example, you might want to exclude your Applications folder from backups, and just reinstall apps from their original CDs if you drive kicks the bucket or if you upgrade later. Click the Options button in the Time Machine preferences window and add files and folders to the "Do not back up" list by clicking the + (plus sign) button. To exclude your Applications folder, select your Mac's hard drive, then the Applications folder, and click Exclude.

If you change your mind later, you can always remove items from this list by clicking the - (minus) button, and those items will be included in the next backup.

When your first Time Machine backup starts, a new window appears on your desktop to let you know things are going. You can close System Preferences now; it won't affect the backup.

4. Ready, Set, Wait
Expect the first backup to take a long time since everything on your Mac is being copied. After the first backup, Time Machine will automatically back up incremental changes to your files every hour for as long as you leave the backup drive connected to your Mac. Future backups will only copy files that are new or have changed, so they'll take less time.

In Time Machine's preferences window, you’ll see the option to show Time Machine's status in the menu bar. Time Machine’s menu bar icon lets you access Time Machine preferences and perform backups any time you want, so you don’t have to wait to back up important files.

5. Understand how Time Machine "thinks."
After a while, your backup drive will fill up, and Time Machine will need to delete your oldest backups to make room for new ones. Time Machine handles this automatically.

Now, if you accidentally delete an important file, all you have to do is click the Time Machine icon in your Dock or the menu bar to enter Time Machine and retrieve the file. Entering Time Machine replaces the Desktop with an outer space background and Finder windows stretching into infinity. Despite all these special effects, finding backed up files is easy.

The front Finder window shows what's currently on your Mac--note that in the screenshot below, though it's very tiny, the bar at the bottom of the screen reads Today(Now), and there’s nothing on the Desktop.

All the Finder windows behind the first one are earlier backups--you can always tell where you are in your backup history by looking at the bar at the bottom of the screen or at the chart on the far right.

Using the arrows at the bottom of the Time Machine screen, you can navigate to the last time a file was backed up. Once you find a missing file--in this case, on the Desktop at "Today at 12:33 PM"--single-click it, and then click the Restore button at the bottom right to copy the file from your backup drive to your Mac's hard drive.

Because Time Machine uses a Finder window, you can navigate to any folder to retrieve files, not just what's on the Desktop. Also, notice that in the screenshots shown previously, the Applications and Utilities icons in the Finder window's sidebar are grayed out. Those folders are unavailable to Time Machine because they weren’t included in the backup, as described in Step 2.

You are now a full-fledged member of Backup Club, so you can breathe a little easier... just don’t forget the first rule!