There's loads of stuff on the 'net about backing up. A Google search
will find plenty of information!
tar's a bit long in the tooth now and not best-of-breed except for simple requirements. I use dar which is Disk ARchiver as opposed to Tape ARchiver. Robust and powerful.
I don't know rsynch but understand it synchronises source and backup files -- which means a file deleted on the source system would also be deleted on the backup system. Fine until you find out a month later that it's been deleted and you want it back. Am I right rsync experts?