Lightroom does not make backups of your original photos, except at Import. So you need to use a third party backup solution -- as far as I know Time Machine works fine -- to back up your photos.
The catalog itself can be backed up by setting the proper option in Lightroom. Under Catalog Settings, there is a backup option. You want to set it to make backups at the desired frequency (the choice is up to you), and when Lightroom asks you if you want to make a backup, choose a location on the external drive.
I suggest Carbon Copy Cloner
As dj_paige says, you can make backups of your photos at import but i can`t recommend it .
Thank you both for your help..
But another question comes to mind;
What is the difference between LR Catalog Settings for your back location of your Catalog and the LR Box that appears when you exit LR (it too offers a location for your Catalog Backup)?
There is no such thing as LR Catalog Settings "for your back location of your catalog". You can only set the frequency of backups under Catalog Settings.
I keep all my photos on an External Hard Drive rather than the computer Hard Drive and use Super Duper by Shirt Pocket for auto backup to a second hard drive for a Mac. SuperDuper!
If both EHDs are kept in your home next to the computer, you are not protected from home disasters than can wipe out both drives.
You might consider cloud back up as another method, such as CrashPlan, which offers unlimited storage for about $60 per year.