Backup files are in the tar+gzip format, with file names relative to the Jenkins home directory. Example of restoring a backup using Linux (GNU tar) syntax:

$ cd $JENKINS_HOME
$ tar xvfz /backups/jenkins/backup-daily-13.tar.gz
config.xml
jobs/myjob/config.xml
...

$JENKINS_HOME is relocatable, meaning you don’t have to restore the backup into the same instance it was created from. This allows you to exercise the backup restore steps by creating a different Jenkins instance on your own computer and restoring things there.