How to back up ?

There are several backup methods available in Discover (typing Backup in the search field will show the available packages), one of the most powerful is using rsync on the command line which is installed by default. If you want to use a graphical interface, luckyBackup is the graphical frontend for rsync.

Just keep in mind that the tool of your choice also depends on the media you choose for doing backups, reading some instructions is highly recommended, as a meaningful backup should always include system configuration files which can only been done correctly with superuser rights. Media verification is also recommended, etc. There is no simple answer to a very complex theme I fear.