smnirosh
Yes you do need to read the manual, I think you are being a bit lazy to ask questions that are answered elsewhere.
Also read the excellent Howtos & FAQ as there is a lot of additional information that adds to or supports what has been written in the official Manual(s). Links to all these are at the top of the Forum.
I bought an external usb hard disk for the weekly fullbackup purpose.
What is the correct file system for that hard disk and what is the most successful command to accomplish this fullbackup weekly.
See
http://wiki.contribs.org/USBDisksparticularly the section on Formatting your USB disk
I strongly advise you to use
ext3 or ext4, much more robust.
In brief,
To configure a regular backup, do this in the server manager, Backup or Restore panel, & select Backup to workstation (which also includes backup to connected USB drives).
Configure for a full backup once a week. Alternatively you can configure for a full backup & then daily incrementals & only connect the drive on the day/night you want a backup done.