Debian OS Backup

[Jacob Ramirez]

We are running linux with Debian OS.  I am new to using linux and
debian.  Can I use an external hard drive to backup the operating system
and files on our linux servers?  If so, how do I create a full backup of
the system for disaster recovery?  Is it easy to restore if there is a
need?
Is there documentation somewhere that I can read that explains how to do
this?  Thanks for your help in advance.
 
Jacob